Pibrary of the Museum
Or
‘COMPARATIVE ZOOLOGY,
AT TARVARD COLLEGE, CAMBRIDGE, MASS.
Founded by private subscription, (nr 1861.
Deposited by ALEX. AGASSIZ. No. [Fe /.
QUARTERLY JOURNAL
MICROSCOPICAL SCIENCE,
EDITED BY
EDWIN LANKESTER, M.D., F.R.S., F.L.S., AND
GEORGE BUSK, F.R.C.S.E., F.R.S., F.LS.
VOLUME ILL
With Allustrations on Wood und Stone.
LONDON:
SAMUEL HIGHLEY, 32, FLEET STREET. om) S55,
LONDON: PRINTED BY W. CLOWES AND SONS, STAMFORD STREET.
INDEX TO JOURNAL.
VOLUME IiIl.
A.
Achromatic condenser, J. D. Sollitt on a new, 87.
Ayres, Dr. P. B., microchemical re- searches on the digestion of starch and amylaceous foods, 247.
Allman, G. J., on Aphanizomenon Flos-aque and a species of Peri- dinea, 21.
on the occurrence among the Infusoria of peculiar organs resembling thread-cells, 177. Amphiprora vitrea B? 40, Amphitetras favosa, 93. ss Wilkesii, 93. Amphora angularis, 39. A Arcus, 39. ee incurva, 39.
Anacharis Alsinastrum, on the cireu- lation of the sap, by F. H. Wenham, Aaale
Angular aperture of object-glasses, F. d’Alquen on a paper by Dr. Grif- fiths on the, 43,
Aperture of object-glasses, J. D. Sol- litt on the, 85. In reply to Mr. Wenham and Dr. Robinson, 239.
5 F, H.Wen- ham on, in reply to Mr. Sollitt, 160,
3 os on the, 302.
Aperture of objectives, on the mea- surement of the, by J. R. Robinson, D.D., 163.
Aphanizomenon Flos-aque, G. J. All- man on, 21.
Arcyria, threads of, 20.
Artificial light, prevention of the glare from, Ferguson Branson, M.D., on the, 173.
Arts, Society of, Prizes offered by the, for cheap microscopes, 234, 306.
VOL, Il.
Atlantic, microscopic examination of deep soundings from the, by J. W. Bailey, 89.
Aulacodiscus Oreganus, 93.
B.
Bacterium termo, Cohn on, 206.
Bailey, J. W., and Prof. W. Harvey, description of new species of Dia- ‘tomacee, 93.
microscopic examina- tion of deep soundings from the Atlantic, 89.
on some new localities for fossil Diatomacee, 91.
Bennett, J. H., on the structure of the Torbane Hill mineral and of various kinds of coal, 185.
Bleakley, E., M.D., on Powell and Lealand’s new condenser, 92.
Blood-cells, action of urea on, 289.
Branson, F., M.D., on the prevention of glare from artificial light, 173.
3 on the circulation of sap, 274.
Bridgman, W. K., on another ‘finder’ for the microscope, 237.
Busch, Dr. W., on Noctiluca miliaris, 199%
C.
Calex Mosquito, C. Johnston, M.D., on the auditory apparatus of, 97. Campanularia geniculata, on the male
reproductive organs of, by Dr. Max. S. Schultze, 59. Campylodiscus clypeus, R. Wigham on, 243. Kiitzingii, 93. Car penter, W.B., review of principles of comparative ’ physiology, 2b: 4
A
326
Cellulose in animals, by R. Virchow, 284,
Chytridium, Cohn on, 207.
Cilia in the Diatomacee, J. Hogg on, 235,
5, on the surface of Conferve, Dr. G. H. Kingsley on, 243.
Circulation of the sap in the leaf-cells of the Anacharis Alsinastrum, by F. H. Wenham, 277.
Closterium Lunula, 8. G. Osborne on the economy of, 54.
“, structure of, F.G. Wright, M.D., on the, 171. Cocconeis costata, 39. » parmula, 93. Eas rhombifera, 94. » suleata, 94. a speciosa, 59. 3 transversalis, 39.
Cohn, Dr. F., researches on the de- velopment of microscopic Algz and Fungi, 202.
Colouration of the China Sea, Camille Dareste on the, 66.
Condenser, new. Powell and Lea- land’s, Dr, Bleakley on, 92.
Confervee, cilia on the surface of, 243.
Conversaziones, Microscopical, 303.
Cornea, compound of insects, 9. *
Currey, Frederick, on the reproduc- tive organs of Fungi, 2638.
A on the spiral threads of the genus Trichea, 15.
Cutaneous follicles of the toad, on the structure of, by George Rainey, 257.
Cymbella truncata, 38.
D.
Dareste, Camille, on the colouration of the China Sea, 66.
Deep soundings from the Atlantic, microscopic examination of, by J. W. Bailey, 89.
Delicate test-objects, definition of, E. L. on the, 233.
Diascope, a new optical instrument, description of, 1.
Diatomacew, cilia in the, J. Hogg on, 235.
Diatomaceous deposits in the mud of Milford Haven, description of, and mode of procuring, by Fitzmaurice Okeden, 26.
if, earths and elays, mode of washing, F, Okeden on a, 158.
“5 exuvie contained in a |
post tertiary lacustrine sand from Glenshira, 30.
INDEX TO JOURNAL.
Diatomacee fossil, new localities for, J. W. Bailey on some, 91.
3 on washing and concen- trating of, Dr. H. Munro on the, 241.
x8 new species of, descrip- tion of, by Prof. W. Harvey and J. W. Bailey, 93.
Diatomacez, on the determination of species in, the Rev. W. Smith on the, 130.
55 on species of, 307.
Discopora ciliata, 256.
D’Alquen, F., on Griffiths’ paper on the angular aperture of object- glasses, 43.
E.
Enamel and dentine of the teeth, T. H. Huxley on, in reply to E. Lent, 127.
Enlargement and multiplication of the images of objects when viewed through small apertures, J. Gorham on the, 1.
Ereolani and Vella.on the develop- ment and life of the Nematoidea, 73.
Eunotia falx, 38.
Eupodiscus? Ralfsii, B, 39.
F.
‘Finder’ for the microscope, on an improved, by F. Okeden, €.E., 166.
5 for the microscope, W. K. Bridgman on another, 237.
Finders, 314.
Flies’ feet, on, 312.
Freshwater marls and_ limestones, microscopical structure of, H. C. Sorbey on the, 95.
Fungi, the reproductive organs of, by F. Currey, 263.
G.
Geological Society, proceedings of, 95.
Glaisher, J., on snow-crystals, 179.
Glare from artificial hght, ou the prevention of, 173.
Glenshira deposit, Diatomaceous exu- vie in, 30.
Gonium pectorale, Cohn on, 212.
Gorham, J.. on the magnifying power of short spaces, 1.
Gregory, W., on diatomaceous exuviz contained in a post tertiary lacus- trine sand, from Gleushira, 30.
Griffith, Dr. J. W., on the angular aperture of object-glasses, 43.
INDEX TO JOURNAL.
H.
Hepworth, John, memoranda by, 312.
Histology, Quekett’s lectures on, re- view of, 75.
Hodgson, W., on an easy method of wiping thin glass covers, 243.
Hogg, Jabez, on cilia in the Diato- macee, 235.
Hunt, G., description of a curious effect of moisture on the markings of Pleurosigma, 174.
5 on the markings of the Pleurosigma, 232. Huxley, T. H., on Noctiluca miliaris,
i on the enamel and dentine of the teeth, 127. Hyalosira punctata, 94.
Is
Illumination, new mode of, by Dr. T.
G. Wright, 236.
= of microscopic objects, F. H. Wenham on the, in reply to Mr. Rainey, 87.
Impressions, metallic, of microscopic objects, mode of obtaining, F. H. Wenham on a, 244,
Infusory animalcules, physiological studies respecting the, by Paul Laurent, 156.
Infusoria, on the occurrence among the, of peculiar organs resembling thread-cells, by G. J. Allman, 177.
Insects, feet and wings of, J. Tyrrell on the, 230.
a $5 by J. Hep- worth, 312.
Isthmia minima, 94.
J. Johnston, C., M.D., on the auditory apparatus of calex mosquito, 97.
Jungermannia, elaters of, action of sulphuric acid upon, 19.
K,
Keber, F., on the porosity of bodies, |
152. Kingsley, Dr. G. H., on cilia on the surface of Conferva, 243, Kolliker, on the motions of spermatic filaments, 293, 296. » on the action blood-eells, 289. », On lymph corpuscles, 291.
of urea on |
| | |
L.
Lagena Williamsoni, 94.
Laurent, Paul, physiological studies respecting the infusory animalcules, 156.
Lent, Ed., on the enamel and dentine of the teeth, 127.
Lepralia scutulata, 255,
Leydig, Dr. F., on the structure and systematic position of the Rotifera, 136.
Lloyd, W. A., on artificial sea-water in marine aquaria, 315,
Lymph corpuscles, Kolliker on, 291.
M.
Magnetic stage, description of a, by J.B. Spencer, 174.
Magnifying power of short spaces, J. Gorham on the, 1.
Marine aquaria, on the employment of artificial sea-water, 315.
Membranipora Sophie, 255.
Memoranda, by John Hepworth, 312.
Menipea arctica, 254.
Microchemical researches on the di- gestion of starch aud amylaceous foods, by Dr. P. B. Ayres, 247.
Microscope, Dr. H. Schacht on, trans- jated by F. Currey, review of, 219.
Microscopes, cheap, proceedings of the Society of Arts with respect to, 234, 306,
Microscopic Alge and Fungi, re- searches on the development of, by Dr. F. Cohn, 202.
Microscopical Society, proceedings of, 176, 247, 317.
Moleschott, on the motions of Sperma- tozoids, 294.
Monas prodigiosa, 206.
Moreland, Mr., on starch, 319.
Munro, Dr. H., on the washing and concentrating of Diatomacee, 241.
Muscular fibre, on, 318,
N.
Navicula crassa, 41. a gastroides, 40,
5 maxima, 41, es rhombica, 40. 6 birostrata, 40.
Nematoidea, on the development and life of the, 73. Noctiluca miliaris, Dr. W. Busch on, 199, a 3 T. H. Huxley on, 49. oF x Dr. Woodham Webb, on, 102.
328
O.
Okeden, F., on an improved ‘ finder’ for the microscope, 166. ,», on diatomaceous deposits in "the mud of Milford Haven, 26. 55 », on a mode of washing diatomaceous earths and clays, 158. Osborne, S. G., on the economy of Closterium Lunula, 54.
1 Ph
Pathological Anatomy, Manual of, by C. H. Jones, M.D., and E. H. Sieveking, M.D., review of, 155.
Pedicellaria of Echinus miliar is, figure of, 83.
of Sputangus purpureous, figure of, 84.
Peridinea, new species of, G. J. All- man on a, 21.
Physiology, comparative, principles of, W. B. Carpenter, 215.
Pinnularia apiculata, 41,
“5 Gastrum, 41.
Pleurosigma, curious effect of moisture on the markings of, 174.
5 markings of the, G. Hunt on the, 232.
Polythalamia (Foraminifera), M. 8. Schultze on the organization and classification of the, 143.
Porosity of bodies, microscopic re- searches on the, by F. Keber, 152. Post-tertiary lacustrine sand con- taining diatomaceous exuvie, W.
Gregory on, 30.
Powell and Lealand’s new condenser, R. Bleakley, M.D., on, 92.
Pulmonary Consumption, Dr. Theo- philus Thompson’s Lettsomian lec- tures on, review of, 227.
Q.
Quekett’s, J., Lectures of Histology, review of, 75.
R.
Rainey, George, on the cutaneous follicles of the toad, 257.
Redfern, P., M.D., on the Torbane Hill mineral and on other varieties of coal, 106.
Reproductive organs, on the, of cer- tain Fungi, by Frederick Currey, 263.
INDEX TO JOURNAL.
Robinson, J. R., D.D., on the mea- surement of the aperture of objec- tives, 163.
Rotifera, on the structure and sys- tematic position of the, Leydig on, 136.
Royal Society, proceedings of, 247.
Ss
Salicornaria borealis, 254.
Savory, Mr., on muscular fibre, 318.
Sea-water artificial, on the employ- ment of, in marine aquaria, 315.
Sertularia imbricata, 256.
Schacht, Dr. H., on the microscope, 219;
Schultze, Dr. Max. S., on the male reproductive organs of Campanu- laria geniculata, 59.
on the or- ganization and classification of the Polythalamia (Foraminifera), 143.
Smith, the Rev. W., on the determi- nation of species in the Diatomacez, 130.
Snow-crystals, J. Glaisher on, 179.
Sollitt, J. D., on a new achromatic condenser, 87.
ss on the aperture of object-glasses, 85.
Sorbey, H. C., on the microscopical structure of freshwater marls and limestones, 95.
Species of Diatomacez, on, 307.
Spencer, J. B., description of a mag- netic stage, 173.
Spermatic filaments, action of alkalies on, 293, 296,
Spermatozoids, motion of, 294.
Spiral threads of the genus Trichia, Fred. Currey on the, 15.
Starch, Dr. P. B. Ayres, on the diges- tion of, 247.
,, the presence of in the blood, Se dh aueeon on, 168. 5 r, Moreland on, 319. sete s. J., on the presence of starch in the blood, 168. Surirella fastuosa, B, 40. Synedra undulans, 41. 5 vertebra, 41.
fb
Thin glass covers, on an easy method of wiping, by W. Hodgson, 243. Thread-cells, on the occurrence of peculiar organs resembling _ the,
among the Infusoria, 177.
INDEX TO JOURNAL.
Toad, cutaneous follicles of, by George Rainey, 257. Torbane-Hili mineral, and on other varieties of coal, P. Redfern, M.D. on the, 106. structure of, &e., J. H. Bennett on the, 188. Triceratium coneavum, 94. 35 gibbosum, 94. A orientale, 94. a Wilkesii, 94. Trichia, British species of, 21. » on the spiral threads Oe Tby.
Trichia-threads, corrections of mis- |
prints in Mr. Currey’s paper on, 176. on mode of preparing,
21.
Tryblionella constricta, 40.
Tyrrell, J., on the feet and wings of insects, 230.
Tubulipora ventricosa, 256.
Ue Urea, action of, on blood-cells, 289.
Vi.
Vibrionia, Cohn on the nature of, 206. Virchow, R., on cellulose in animals, 284,
| |
329
W.
Ward’s, Mr., conversaziones, 303.
Webb, Woodham, M.D., on Noctiluca meliaris, 102.
Wenham, F. H., on a method of ob- taining metallic impressions of mi- i objects, 244.
on the illumination of microscopic objects, in reply to Mr, Rainey, 87.
+ on the circulation of the sap in Anacharis Alsinastrum, Die
reply to Mr. Sollitt on the aperture of object-glasses, 160.
1: on tests mounted in balsam, 302.
Wigham, R., on Campylodiscus cly- peus, 243.
| Wright, Dr. T. G., on a new mode of
illumination, 236. » F.G.,M.D., on the structure of Closterium, 171.
Z. Zoophytology, 253, 321.
LONDON :
Printed by W. Crowes and Sons, Stamford Street.
QUARTERLY JOURNAL
OF
MICROSCOPICAL SCIENCE.
ORIGINAL COMMUNICATIONS.
On the ENLARGEMENT and Muttipiication of the Imaces of Oxssects, when viewed by the Light admitted through small Apertures ; and on the Diascorr, a new Optical Instrument. By Joun Gornam, M.R.C.S.L., &c.
(Continued from Vol. II., page 234.)
It has been before noticed that less attention has been bestowed upon the investigation of objects that lie near at hand, within an inch or two, we will suppose, of the eye, than upon objects which are placed at a considerable distance from it, that, for example, of as many furlongs. I have also endea- voured to show that small circular perforations made in a card, and rendered semi-transparent, constituted in themselves objects well adapted to illustrate the magnifying power of short spaces, by presenting a rapid and palpable enlargement of the visual angle to the eye ; and, lastly, a series of phenomena has been described, which resulted from viewing small figures held close to the eye in front of such apertures, and rendered visible by the light admitted through them.
The whole subject arranges itself therefore under two dis- tinct divisions, which comprise :—1. An examination of the images formed by viewing objects held zn front of small aper- tures ; and 2. An examination of those images which result from placing the objects behind the apertures.
1. Of images formed when the eye and the object are both on the same side, that is, in front of the apertures.
We have already seen that when bodies not exceeding the diameter of the pupillary opening of the eye are held in close proximity to the visual organ, and are then examined by the light admitted through small inlets about the fortieth of an inch in diameter, their images become maynified, multiplied, and inverted ; and further, that they are illuminated with light
VOL. ITI. B
2 GORHAM, ON THE
of an intensity varying with the number of apertures employed to render them visible.
This light, be it observed, is always simply transmitted ; never being "reflected nor refracted by the intervention of glass, or ts: any other substance having catoptric or dioptric effects. The apparatus required in these experiments there- fore is éssentially very simple and uncomplicated, consisting indeed of a mere short tube open at one end, and haying a plane, perforated with small holes to admit ihe light, at the other; while the object to be examined is applied at the open end, and held as close to the eye as possible. Hence a pill- box and a narrow slip of glass constitute all that is really necessary to explain the laws which are in operation, and to give an idea of the phenomena which are involved in their successful application.
From the remarks made in a previous section, it is obvious that these phenomena are owing to the size, and to the intervals of the apertures themselves, and to their distance with respect to the eye. Thus their size should be the one-fortieth of an inch,—their intervals the one-tenth of an inch,—and their distance from the eye from one to two inches. If these con- ditions are not fulfilled, the images become either undefined or dimly illuminated ; but when they are strictly observed, the combinations, which an instrument constructed upon such prin- ciples is capable of presenting to the eye, are very beautiful.
But a mere tube of pasteboard, however well it might answer for a first experiment, is inefficient, for it is difficult to retain the slip of glass in its proper position between the tube and the eye. It was essential therefore to construct a small instrument of some more solid and durable material, such as wood or ivory, with which experiments might be conveniently performed.
This instrument consists of a tube, T, one or two inches long, and about one inch thick, expanding at the end to which the eye is applied into a circular lip, L, which is about one’ inch and a half in diameter, while that of the round opening in its centre » is about half an inch. This end is provided with a slit sufficiently large to permit a thin narrow slip of glass, about an inch broad, to slide easily through it, as Steen in the figure. The other end:has/a\ circular rim, R,
MAGNIFYING POWER OF SHORT SPACES. 3
which revolves in the groove, G, and to this rim is attached a second rim, 7, which is provided with a female screw, and this secures any circular plane of apertures, p, we may choose to insert, at the same time that it admits of its revolution.
A series of objects, either painted or mounted on glass slides, can thus be examined at one end by the light admitted through perforated planes at the other. As such an optical contrivance is a mere conductor of the light directly from the apertures to the eye, while at the same time it excludes all the extraneous rays, it may not inaptly and for convenience’ sake be denomi- nated a diascope: a term derived from the two Greek words, dia, through, and cxomew, I view. And when it is used for the purpose of multiplying images, it may be called the mui- tiplying diascope.
The circular planes containing the apertures are made of thick pasteboard, perforated with a needle at intervals of the one-tenth ef an inch as before stated; and the openings may be arranged in a variety of combinations, as shown in the patterns from one to six, page 225, of the last paper.
Here let us notice that the round form of the images, de- picted on the retina when examining small apertures in this way, is determined by the shape of the pupillary opening of the eye rather than by that of the apertures themselves. Hence it is always circular whether these be round, triangular, square, or altogether irregular in outline. ‘This can easily be proved by perforating cards with triangular or square needles, The openings thus made when brought very near to the eye always appear circular. A little reflection will show that this is a necessary result, inasmuch as the outermost rays of the rapidly-diverging cones are intercepted by the zrzs, while the more internal rays pass on through the pupil, thus receiving their circular form.
Hence if the pupil be widely expanded the discs will be large, and vice versd, but nevertheless always perfectly round.
Let us now take a circular plane, presenting a combination of perforations arranged as to colour and relative position as in the outline, No. 4, page 225, of the last paper; and let us notice what kinds of images are presented to the eye when small bodies are examined by the light transmitted through them.
Holding the instrument to the eye with a view to examine the apertures, we observe that the smallest particle of dust, or film of mucus, happening to exist on the surface of the transparent cornea, is immediately detected; and although such bodies have no definite shape, they are to be recognised interfering with the transparency of the discs, and forming an
BZ
4 GORHAM, ON THE
opaque spot or streak which occupies exactly the same posi- tion in each. Similar results are obtained if a small dot, no bigger than a pin’s head, be made on a slip of glass with Indian ink, and introduced into the eye-piece of the diascope. The dot now appears multiplied, and as many images of it are seen as there are apertures by which it is made visible.
In like manner if a small semicircle be painted on glass, its images will be multiplied, but each image will be seen in- verted, and will appear as a black body on an illuminated and coloured ground.
And if a small triangle, or any other figure of definite shape, be cut from a piece of black paper, and if the opening thus made be examined in the same way, a number of illumi- nated and coloured triangles will be seen on a black ground.
It is when transparent figures are made according to this last method that really beautiful combinations may be produced. But here, in order to insure success, it is necessary that the transparent openings should never exceed in size the pupillary aperture of the eye, fig. 16. Hence they should always be made within the limits of a circle, the 0°18 of an inch in diameter, fig. 15; this being the mean of the greatest and least
Fig. 15. Fig. 16.
o &
expansion of the pupil. If such transparent figures are made greater than this, the margin of the pupil will obstruct some of the external rays, and the outline of the image will thus be lost or badly defined. If, on the other hand, they are less, the quantity of light admitted into the eye will be too small, and the images but feebly illuminated.
Such openings used as objects are to be considered as little else than artificial pupils, modifying the shape and contracting the size of every cone of light which is admitted into the eye from small apertures,
When one of these transparent openings is held close to the eye, and examined with common diffused light, it becomes altogether invisible ; but, when it is viewed by the aid of a pencil of light from a small inlet, its outline is well defined and much magnified ; and the disc of the inlet, which would otherwise be circular, is replaced by the pattern we may choose to give to the transparency.
And if the pupil of the eye itself, obliterated, as it often is, from disease, have a small portion excised from it, as in
MAGNIFYING POWER OF SHORT SPACES. +)
the operation for artificial pupil, the newly-formed opening will appear inverted and multiplied in the same way; and each image, instead of being circular as it is in the healthy eye, will be seen to resemble the figure of the new and dis- torted pupil.
But in order to demonstrate the images which this instru- ment is capable of presenting to the eye in the most satisfac- tory manner ; instead of cutting holes in pieces of black paper, a series of figures having a transparent body and a black out- line may be painted on glass with Indian mk. For this purpose round patches of Pale about the size of a fourpenny piece, should be laid on the centre of each glass slip with a camel’s-hair pencil ; and, when dry, transparent figures of the required shape and cintewsrons can easily be Higdes by erasing a portion of the ink with a finely-pointed and slightly-moist- ened wooden style.
The forms of such transparencies will suggest themselves to the ingenuity of the reader, but a few are subjoined by way
of example (figs. 18 to 33).
Fig.18. 19 2 25.
Fig. 18. Regular hexagon. | Fig. 28. Two semicircles. 4, JIS Hexagonal star. | ,, 29. Triangle and semicircle. », 20. Rhomb of 60°. | ,, 380. Curved and straight lines », 21. Curved triangle. | intersecting at 60°. », 22. Ditto. | ,, 31. Three lines intersecting at », 23. Trefoil. | 60°. » 24. Circle. » o2. Two curved lines inter- », 25. Concentric circles. | secting at 60°. », 26. Triradiate star of 120°. ,, oo. Two angles of 60° inter- », 27. Straight lines intersecting secting.
at 60°,
Such forms arrange themselves into two groups; those, for instance, which are entire in themselves, and which constitute elegant ‘designs by their multiplication. and the shifting of their Pere position (figs. 18 to 25), and those again which are imperfect figures, but which produce entire compositions of great beauty by their combination (figs. 26 to 33).
6 GORHAM, ON THE
As the apertures are arranged in lines which cross each other at angles of 60° and 120°, the outlines of the transparent figures should bear the same angular relation. Thus the modifications of the equilateral triangle, the rhomb of 60° and 120’, and the regular hexagon, a few of which are given in the above examples, are well suited for the purpose.
When a transparent hexagonal star (fig. 19), slid into the eye-piece of the instrument and brought close to the eye, is examined by the light admitted faces a combination of apertures, that, for instance, marked No. 4, at the 225th page, placed at the other end, the images of a number of stars are apparent. ‘These stars are seen to change their relative position with every movement, however slight, of the revolving plane. Sometimes they are observed to touch each other by one ray, at others by two, while in intermediate positions the rays alternate. The patterns which are thus formed are as variable as the parts into which a circle can be divided. ‘They are shown in two of their phases of revolu- tion in the 4th and 5th figures of Plate VIII., Vol. IL.
The concentric circles, fig. 25, thus multiplied display themselves with good effect. Their appearance is represented in the 6th figure of Plate VIII., which is produced by using the arrangement of apertures marked No. 5, page 225.
But the combinations effected by the mutual coalescence of the images of the imperfect figures into one entire composite form are the most curious. Thus if the three-rayed star, fig. 26, be examined, its images will be seen either to alter- nate (fig. 9, Plate I., Vol. IIL.), or to resolve into one hexa- gonal reticulation with a dot in the centre of each mesh, as shown in fig. 10, Plate I., Vol. III. And the images of the figure, composed of the straight and curved lines, fig. 30, unite into many fresh devices; two of which are copied in the figures 7 and 8, Plate I.
But it is needless to multiply examples, as those which have been already given will doubtless have sufficed to explain the construction of the instrument, and one of the purposes at least to which it may be legitimately applied.
Hitherto we have confined our attention chiefly to the mu/- tiplication of the images of artificial objects prepared expressly for the purpose, and viewed by the aid of the light admitted through small apertures.
We are now to consider how the images of natural objects are magnified by the same means.
Here let us notice, in limine, that we are not about to insti- tute a comparison between two optical instruments, the eye and the achromatic microscope, which although they are con-
lod
MAGNIFYING POWER OF SHORT SPACES. (
structed on the same principles are yet totally different as to their uses. The healthy visual organ, itself a perfect instru- ment, ‘ converses with its objects” at almost all distances, and assists the other senses in becoming acquainted with the form, position, and magnitude of material substances. The microscope, on the other hand, all but a perfect instrument, enables us to see clearly and to examine certain objects, which from their small size and without its aid would be indistinct, if not altogether invisible, It is restricted to the small size and the short distance of its objects, and from its very construction it has magnifymg powers which the eye neither possesses nor requires. If the eye were endowed with these, therefore, to the exclusion of its self-adjusting properties, whereby it discerns common objects in the ordinary way at great and small distances, it would be rendered com- paratively useless as a visual organ.
Hence it were folly to attempt to invest this organ with functions, the possession of which would subject its owner to the greatest inconvenience. An exemplification of this position occurs to me in the case of short-sighted persons,
When therefore we find ourselves enabled by a carefully- devised experiment to detect, with the naked eye, certain configurations upon or within an object which, we may sup- pose, has never before yielded an image at all excepting through the medium of a lens, we are not to imagine that we are thereby infringing on the domains of the microscope, which being constructed for this very purpose would present us, perhaps, with an image ten thousand times as large and distinct. But putting this instrument altogether out of con- sideration, and throwing aside all extraneous assistance, we are the rather to consider how the eye, which has certain limits to distinct vision for short distances, can yet adjust itself for spaces still smaller, and in so doing become con- verted into a kind of natural magnifying glass.
We have now therefore to turn our attention to certain microscopic objects, which are to be examined and resolved without a lens of any description; and we are stimulated to an investigation of this kind by recollecting what has been already attained with respect to the magnitude of the images of small apertures themselves, when placed under circum- stances the most favourable for their inspection. Amongst these we cannot fail to have noticed at least two conditions necessary to be fulfilled in such investigations, viz.—First, that the object be held very near to the eye; and secondly, that every ray of light, excepting what is required to illumi- nate the object, be carefully excluded. The first insures an
8 GORHAM, ON THE
enlarged image, whilst the second prevents a too great con- traction of the pupillary opening. Hence the necessity for examining objects through small darkened tubes, and hence, too, the necessity for closing the eye which is not engaged in exploring.
Again, we must not overlook the fact, that in using a small aperture for the purpose of examining any transparent sub- stance there are two methods which may be employed. By. the one, the object is viewed through the aperture; by the other, the aperture is viewed through the object. The former has been almost always adopted by the curious, the latter scarcely ever. It is capable, however, as these papers show, of eliciting so many phenomena peculiar to itself, that I am surprised it has not been frequently used, and the results carefully investigated. Each of these plans throws a different picture on the retina of the eye, and of this the transparent animal membrane chosen for the following experiments will afford, when examined in both ways, abundant exemplification.
For the purpose of presenting very small objects, mounted on microscopic slides in the usual way, before the eye at small distances behind a minute aperture, and to exclude the surrounding rays of light, I took an upright box of pasteboard about one inch and a half deep, and one inch and a quarter in diameter, and having cut a couple of slits through one of its sides sufficiently large to admit of a slip of glass an inch broad sliding to and fro, I made two small apertures opposite to each other, the first the one-thirtieth of an inch, and the second the one-fourth of an inch in diameter ; and these were so disposed, that when the glass slip with a small object
mounted on its centre was introduced through the slits, the two apertures and the object were all in one straight line ; while the slide was about a quarter of an inch behind the smaller opening, see fig. 34.
MAGNIFYING POWER OF SHORT SPACES. 9
With this simple apparatus I could examine very small transparent objects at pleasure, either by the light of the sun or of a taper. Whilst, however, it has been thought better to notice the dimensions of the apertures, &c., for the conveni- ence of others who might wish to repeat the experiments, it must not, by any means, be supposed that they are the best adapted to insure success, or that better could not be devised.
Having been engaged in the preparation of 1 series of dis- sections of the compound cornea of the eye in insects, I naturally subjected one of these beautiful objects to the first experiment in my lens-less microscope. Here, however, for the informa- tion of those who may not be conversant with these objects, or the peculiarities of their structure, it may be remarked that the roundish, prominent, transparent elevations observed, generally one on each side of an insect’s head, constitute the membrane in question. This membrane forms at once the defence and the covering to the delicate parts in the interior of the eye, as well as ihe transparent medium by which the light is admitted into this tiny organ. It is analogous, more- over, to the transparent cornea of the eye in the higher iclacces of animals in being transparent, composed of several firmly- adhering layers, and forming the outermost of all the coverings of the eye. But it is altogether dissimilar in this respect, that it is found to consist of an immense number of facets or little pieces lying, side by side, like fine mosaic; and which from being of a regular hexagonal shape, and arranged in perfect order, present when examined under the microscope an appearance like a honeycomb. Hence it has received the name of compound cornea.
The eye of the large insect, called the dragon-fly, is recom- mended for a first trial in dissection, because it is not only very large but exceedingly beautiful. The compound cornea is at once separated from the rest of the eye with a pair of finely-pointed scissors, and the dark thick pigment which fills the inside is then washed away by soaking in a tumbler of cold water for an hour or two, and then using a camel’s-hair pencil. ‘To procure it in a perfectly clean and transparent state, however, it is better to wash and rewash it after macera- tion for two days in frequently-changed cold water. Then, while still moist, let small circular pieces be excised with a small punch, and pressed immediately between two slips of glass. In a few days they will have become dry and flat, and may then be mounted in what is called the dry way, as if for the microscope.
I wish it was in my power to convey to my readers an idea of the great beauty of one of these specimens ; to say nothing
10 GORHAM, ON THE
of the wonderful arrangement whereby upwards of twelve thousand planes, each a perfect hexagon, are packed in a bit of membrane scarcely so large as half the little finger nail, ‘“‘] have often,” says the celebrated Leeuwenhoek, “ made re- peated dissections of the eyes of various kinds of insects, merely on account of the pleasure the contemplating them afforded me.”* But few, however, seem inclined to investi- gate these subjects for ‘themselves, trusting rather to that second-hand kind of knowledge derivable from books. This distaste for exploring the works of nature may possibly, in some instances, commence with the limited resources of the pocket ; the very preparation of a microscopic object in- volving the necessity for a costly instrument wherewith to investigate it. If, however, I shall succeed in pointing out certain beauties peculiar to the compound cornea in the eye of the insect, which may be discovered with the naked eye, and without a microscope, this membrane will have become invested with a new interest, and thus others may be stimu- lated to a like inquiry. But to return. Having inserted a slide containing a circular section of the eye of the dragon-fly in the box prepared for the purpose, I proceeded to examine it. Recalling to mind, however, that each of the hexagonal facets is barely the six-hundredth of an inch across, and that many hundreds of such facets are contained in the smallest section, it was much to anticipate that such a structure should be 7esolved by a process so simple ; and when on viewing the membrane, by looking at it through the small aperture, while a lighted amie was held nearly close to the larger one, it presented a semi-opaque and altogether homogeneous appear- ance, I had almost concluded that my efforts were frustrated. To overcome the difficulty was reserved, however, for a future trial. Now if, instead of a candle, a small wax taper be used, and if this be held at the distance of from five-to nine feen rather than close to the large aperture, a beautiful sight pre- sents itself. Instead of the flame of one taper, there: are exhibited the miniature images of the flames of many tapers; and these are not only very definite in their outline so as to be immediately identified, but they are arranged at regular intervals, But, what is still more curious, each image, except the central one, is seen to be composed of the colours of the prismatic spectrum,—violet, indigo, blue, green, yellow, orange, and red; of which the extreme tints are so disposed that the blue portion in each image is always nearest to the central or colourless flame, and the red the most remote from it. Hence the blue and the red tints alternate in concentric
* Leeuwenhoek, vol. ii. p. 341.
MAGNIFYING POWER OF SHORT SPACES. 11
circles. When the images which are most distinct, for those near the margin look fainter, assume in the aggregate the form of the hexagonal star, which they not unfrequently do, the appearance is striking and uncommon, see fig. 11, Plate I.
The simplicity of the process by which such a spectacle is produced, together with the novelty of the sight itself, did not tend, of course, to diminish the sense of its gorgeousness ; and I was delighted to find a natural multiplying glass in a tissue, which had already contributed so much to my ad- miration and wonder when examined under a compound microscope.
On viewing the sun in the same way, each small and per- fectly circular image presented the rainbow tints in the same order, as in fig. 12, Plate I., and the multiplied images of the pale moon were scarcely less beautiful.
I may remark, in passing, that the taper flame and the image of the moon were seen through a specimen mounted in Canada balsam ; but the rays of the sun were less distressing to the eye when examined through a specimen mounted in the dry way.
Thus, although I had not, in this experiment at least, suc- ceeded in rendering visible a magnified image of each hexagon in outline, which indeed was the object of my research, I had, in effect, resolved the reticulated structure of the membrane; for in this way only could the peculiarities of a multiplying medium have presented themselves. The interval between each image served, moreover, to indicate the apparent enlarge- ment of each facet, and thus to give a notion of the magnify- ing power of short spaces.
Still bearing in mind the comparatively enormous magni- tude imparted to images on bringing the objects which pro- duce them very near to the eye, and recollecting that the image of a mere needle-puncture seen at half an inch is magnified no less than a million times, it was difficult to renounce the idea of the practicability of defining the hexagonal lattice- work of an insect’s eye with the naked eye, and without the assistance of a material lens.
In the former attempt the membrane seemed too opaque to disclose its minute internal configuration, a specimen was therefore now mounted in balsam to increase its transparency. This, however, did not succeed; on the contrary, it had become so indistinct that its structure could now be scarcely made out even with a microscope. In order to define the hexagons it was evidently necessary to colour the membrane. A few specimens