Gambar halaman
PDF
ePub

higher dispersive power, or a higher refractive index with a relatively lower dispersive power. It would then be possible by proper combination of such materials with the usual crown and flint glass, to partly remove the chromatic and spherical aberrations, independently of each other, and thus fulfil the essential conditions on which the removal of the chromatic difference depends.

As the defects of the present objectives, in regard to the chromatic as well as the spherical aberration, originate in the optical properties of the substances on which the optical art of the day is based, the further perfecting of the Microscope in its dioptrical working, is therefore chiefly dependent on the progress of the art of glass-making, and will in particular require, that new kinds of glass should be produced, which admit of a better correction of the so-called secondary spectrum and which show a different relation of the refractive to the dispersive power than at present has been obtained.

The hope that such claims can be satisfied, in the more or less distant future, and the way opened for a substantial perfecting of the Microscope, as well as of the other optical instruments, rests on thoroughly established facts. The mode in which, in the kinds of glass now used, the indications of refraction and of chromatic dispersion appear, need not be considered as a natural necessity. For a sufficient number of different transparent substances may be chosen from amongst natural minerals and out of the many artificially formed chemical compounds, which offer essentially different properties as regards their refraction and chromatic dispersion, only that in other respects they are not adapted for optical use. Experiments for the manufacture of glass with less secondary dispersion, which were undertaken several years ago in England, with the co-operation of Prof. Stokes, although they were without practical result, gave noteworthy suggestions on the specific effect of certain bases and acids on the refractive properties. The uniformity which the present kinds of glass show in their optical properties, is to be attributed to the fact that the glass factories have hitherto used only a small number of materials, scarcely any other than aluminium and thallium, besides silica, alkali, lime, and lead, and we might reckon with some confidence on a greater variety of production, if only the glass manufacturers, led by methodical study of the optical properties of various chemical elements in their combinations, would leave that very limited field.

Unfortunately there seems little hope under present circumstances of any important advance in this direction in the immediate future. The present prospect, on the contrary, indicates a state of affairs which endangers many scientific interests. The manufacture of optical glass has been for a long time not far removed from a kind of monopoly; at least the art is in the hands of so few, that competition is out of the question. Since Daguet's glass-works were closed, there are now only two such institutions, which supply the general demand, while the third, founded by Utzschneider aud Fraunhoferthe only one in Germany-has remained exclusively in the service of one optical workshop. It must, it is true, be admitted that this art has made very important progress in many respects during the last

thirty years. Not only are the present kinds of crown and flint glass produced in formerly unattained perfection, as regards purity, homogeneity, and freedom from colour, but the whole series of optical glass has been widely extended in one direction by the manufacture of flint glass which considerably surpasses the previous kinds in high refractive power and dispersion. This progress, however, is all in the direction of inherited tradition. The art of glass-making has not apparently started on a fresh path, to enrich practical optics with new materials, and from the lack of earnest competition, the business interests of the proprietors of this manufacture do not offer any special incentive to the pursuit of ends which do not promise them assured advantages. Further, let us reflect how dangerous it is, that a branch of industry so important and so indispensable to many sciences should be in the hands of the few, so to speak, for under these circumstances unfortunate coincidences might threaten its continuance, and occasion a serious calamity. It is therefore a vital question for optical and other sciences interested therein, that in the future more forces should be gathered into the field, and that a keener competition should call forth stronger incentives to progress.

We can scarcely suppose that private initiative will suffice to supply this need without a strong external impulse. Undertakings of this kind are attended with so much difficulty and necessitate so large an outlay for results, which even under favourable circumstances, are so remote, that they can have little attraction even for enterprising people. A great rise in the industry in question can scarcely be expected unless funds are freely granted for its furtherance by Corporations or the State. The field is open here for learned societies which are in a position to offer material help towards the needs of science, to perform a most beneficial and worthy task. For great and various interests are dependent on the increasing efficaciousness and progress of the glass-manufacture. It is not, by any means, the Microscope alone which is here considered, but all arts and sciences dependent on the use of optical resources.

A retrospect of the last portion of this discussion on the ways and means of perfecting the Microscope in the future, shows a more favourable prospect than the earlier considerations. As regards that part of the performance of the Microscope which touches the dioptrical functions of the objectives, an increasing improvement of the instrument in important points may be expected in the future. The difficulties which at present oppose further progress in this respect, and will perhaps long continue to do so, need not in any way be considered as insurmountable. This is the proper field in which optical art may hope to attain further results. The question of the best adapted and most advantageous means of solving the difficulty under consideration is certainly not exhausted either as regards theoretical optics, or those practical arts which co-operate in the work of opticians. Theory may, in time, by a deeper insight into optical problems, point out new methods of removing, more effectually than at present, the chromatic dispersion and spherical aberration in objectives; practical optics may, by the perfecting and refining of the method of

work, render possible a still greater exactness of the mathematical forms which theory seeks to realize, and the art of glass-making may in the future produce new materials instead of those now used, which, in their optical properties, may offer more favourable conditions for the construction of perfect objectives than our present crown and flintglass. Doubtless united efforts in this direction will result in a continual progress towards perfection of construction, which will bring great benefits to the scientific application of the Microscope, if even it does not increase the absolute capacity of performance of the instrument.

In this direction lie the ends attainable. Efforts grounded on a fundamentally different aspect of the question will be thwarted in the future, as in the past, by the barriers which nature opposes to human illusions.

Webb's 'Optics without Mathematics.'-The author of this work makes the astonishing statement that "the magnifying power of the Microscope is more frequently given in superficial measure!" though he considers that "it is better for our purpose to reckon it in the linear form."

BENECKE, B.-Die Anwendung der Photographie zur Abbildung mikroskopischer
Objecte. (The use of photography for representing microscopic objects.)
[Summary of recent papers on the subject by T. C. White, W. H. Walmsley,
G. J. Johnson, R. Hitchcock, C. Kiär, &c.]

Zeitschr. f. Wiss. Mikr., I. (1884) pp. 109-13. BOTTERILL, C.-Protoplasm. (Presidential Address to the Liverpool Microscopical Society.)

Micr. News, IV. (1884) pp. 57–68.

BRADBURY, W.-The Achromatic Object-glass, XXX.

[ocr errors][ocr errors][ocr errors][merged small][ocr errors][merged small][merged small]

Engl. Mech., XXXVIII. (1884) pp. 513-4.

BULLOCH, W. H.-The Congress Nose-piece.

[Reply to A. McCalla infra, agreeing that he suggested the idea, “but it is one thing to suggest an idea and another to put it into practical shape."] Amer. Mon. Micr. Journ., V. (1884) pp. 58-9.

C., J. D.-New Eye-piece Micrometer. [Post.]

D., E. T.-Graphic Microscopy.

II. Eyes of Epeira conica.
III. Palate of Limpet.

Amer. Mon. Micr. Journ., V. (1884) p. 52.

Sci.-Gossip, 1884, pp. 25–6 (1 pl.); pp. 49–50 (1 pl.). Dallinger's (Rev. W. H.) Nomination to the Chair of the Society.

Journ. of Science, VI. (1884) p. 118.

DIPPEL, L.-Mikrographische Mittheilungen. (Microscopical Notes.)
[(1) The formula for a on p. 312 of his 'Handbook of General Micro-
scopy.' (2) Remarks on some test-objects of the genus Grammatophora. (3)
Correction-adjustment with homogeneous immersion objectives.] [Post.];
Zeitschr. f. Wiss. Mikr., I. (1884) pp. 23-33 (1 fig.).

Edison Electric Lamp, Homologous sections and molecules.
Micr. Bull., I. (1884) p. 14.

*See Bibliography, infra, p. 303.

ENGELMANN, T. W.-Das Mikrospectral-photometer, ein Apparat zur quantitativen Mikrospectralanalyse. (The microspectral photometer, an apparatus for quantitative microspectral analysis.) [Post.] Bot. Ztg., XLII. (1884) pp. 81–8. FAWCETT, J. E.-Photomicrography. [An ordinary camera can be used.]

Micr. News, IV. (1884) pp. 52-3. FEUSSNER, K.-Ueber die Prismen zur Polarisation des Lichtes. (On prisms for the polarization of light.) [Post.]

Zeitschr. f. Instrumentenk., IV. (1884) pp. 41-50 (8 figs).
Nature, XXIX. (1884) pp. 514-7 (8 figs.).

FLESCH, M.-Ueber einen heizbaren, zu schnellem Wechsel der Temperatur
geeigneten Objecttisch. (On a hot stage for a rapid change of temperature.)
[Post.]
Zeitsch. f. Wiss. Mikr., I. (1884) pp. 33-8 (1 fig.).
FRANCOTTE, P.-Description d'une Chambre-claire. (Description of a camera
lucida.) [Post.]

Bull. Soc. Belg. Micr., X. (1884) pp. 77–9.

Gauss on the Object-glass. See Mellor, T. K. GILTAY, E.-Theorie der Wirkung und des Gebrauches der Camera Lucida. (Theory of the action and use of the camera lucida.) [Post.]

Zeitschr. f. Wiss. Mikr. (1884) pp. 1-23 (10 figs.).

GRUNOW, J.-The Abbe Illuminator.

[Instructions for using this illuminator as constructed by him.] Amer. Mon. Micr. Journ., V. (1884) pp. 22-3. HERRICK, S. B.-The Wonders of Plant Life under the Microscope. 248 pp. and 85 figs. 16mo, New York, 1883.

HITCHCOCK, R.-The Standard Micrometer of the American Society of Microscopists. [Cf. supra, p. 287.] Amer. Mon. Micr. Journ., V. (1884) pp. 34-5.

[ocr errors]

"Our Advertisers."

[Brief notices of various American opticians.]

[ocr errors]

Amer. Mon. Micr. Journ., V. (1884) pp. 56–7.
Giant Electric Microscope.

[Notes as to the absence of novelty and the unsteadiness of the light.]
Amer. Mon. Micr. Journ., V. (1884) p. 57.

HURD (F.) Portable Microscope.

[Statement only of "a design which he believes will prove satisfactory," packing 5 x 23 x 13 in.]

Amer. Mon. Micr. Journ., V. (1884) pp. 37-8.

Journal of the Royal Microscopical Society, Vol. III.

[Review.]

JULIEN, A.-Immersion Apparatus.

Journ. of Science, VI. (1884) pp. 106-7.

[Title only of paper read at meeting of Society of Naturalists of the Eastern United States.]

Amer. Nat., XVIII. (1884) p. 224.

KAROP, G. C.-Table for Microscopical Purposes. [Soft white wood, 2 ft. 9 in. long, 1 ft. 6 in. wide, and 2 ft. 3 in. high. No cross-bar to the legs in front. Top 1 in. thick, "so that at any time it may be planed afresh if discoloured or eroded by acids." On each side in front is a sliding board to serve as an arm-rest, 6 in. wide and 15 in. apart. A piece of plate glass 7 in. × 6 in. let in the top over a piece of white paper or card. Half the glass blackened behind, and on the card opposite the other half is marked a 3 x 1 space, with centering lines, microscopical measurements, magnifying powers, &c.]

Journ. Quek. Micr. Club, I. (1884) pp. 312-3 (1 fig.).

KITTON, F.-Drawing with the Microscope.

[Objects to E. Holmes' suggestion of placing the slide cover downwards (ante, p. 146) that "the upper and under surfaces of an object are not as a rule alike; a further objection is that all powers exceeding 4/10 could not work through an ordinary_slide." Gives the Wollaston camera the preference over all others tried.]

Sci.-Gossip, 1884, pp. 41.

KNAUER, F.-Das Mikroskop und seine Anwendung. (The Microscope and Naturhistoriker, V. (1883) pp. 525–7 (concl.).

its use.

MAINLAND.-Substitute for a Revolving Table.

[Highly lacquered Japanese tray, 20 in. x 12 in.]

MATTHEWS, J.-Revolving Table.

[Ante, p. 147.]

Journ. Quek. Mier. Club, I. (1884) p. 323.

Journ. Quek. Micr. Club, I. (1884) p. 319.

MCCALLA, A.-The "Congress" Nose-piece.
[Claims to be the original inventor and not W. H. Bulloch.]

[ocr errors][ocr errors]

Amer. Mon. Micr. Journ., V. (1884) pp. 38 9. "Give credit to whom credit is due." [Same subject.]

MELLOR, T. K.- Gauss on the Object-glass.

The Microscope, IV. (1884) pp. 30-3.

Engl. Mech., XXXIX. (1884) pp. 56-7. MICHAEL, A. D.-Polarization of light by a concave mirror of opal glass, or a piece of white china. Journ. Quek. Micr. Club, I. (1884) pp. 323-4.

"Microscopists" and the position of the Microscope. ["The statement is often made that the Microscope owes its present approximation to perfection, and microscopical methods their extensive development, to "microscopists," that term being applied to those who consider the Microscope as an end, not a means, and whose whole use of the instrument is confined to the resolution of test-objects and the study of the marking of diatoms. Nothing is more erroneous. The Microscope is far more in debt to the biologist who uses it as a means to solve some problem. To him we owe all our methods for staining, all our facilities for section-cutting, and every discovery in the use of microchemical reagents."]

"Monachus."-Microscopic Test-Objects.

Science Record, II. (1884) p. 87.

[Reply to L. Wright and E. M. Nelson, infra.]

Engl. Mech., XXXVIII. (1884) pp. 517 and 560. MOORE, A. Y.-Slide of Amphipleura pellucida mounted in a medium of refractive index 2.3. [Infra, p. 319.]

Amer. Mon. Micr. Journ., V. (1884) p. 37.

The Parabola as an Illuminator for Homogeneous immersion
The Microscope, IV. (1884) pp. 27-30 (1 fig.).

Objectives. [Post.]

NELSON, E. M.-Microscopic Test-Objects.

[Reply to (1) Monachus," ante, p. 141—supra, p. 288; (2) T. T., ante, p. 148 ; and (3) L. Wright infra.]

Engl. Mech., XXXVIII. (1884) pp. 516-7 (4 figs.).

Möller's Probe-Platte.

"[Remarks on plates mounted in phosphorus, monobromide, balsam, and dry.] Engl. Mech., XXXVIII. (1884) p. 540.

Microscopic Test-Objects.

"[Further in reply to "Monachus."]

Engl. Mech., XXXVIII. (1884) p. 560 (4 figs.). On the Selection and Use of Microscopical Apparatus.

Resumé of "demonstration" at the Quekett Microscopical Club.]

Engl. Mech., XXXIX. (1884) p. 48.

OLLARD, J. A.-Simple form of Revolving Table made out of two mincing boards. [Exhibition only.]

Journ. Quek. Micr. Club, I. (1884) p. 323.

PELLETAN, J.-Le Microscope "Continental." [Warning against imitations!]

Journ. de Microgr., VIII. (1884) p. 121. PENDLEBURY, C.-Lenses and Systems of Lenses, treated after the manner of Gauss. 95 pp. and 24 figs. 8vo, Cambridge, 1884.

[ocr errors]

PENNY, W. G.-Theory of the Eye-piece. IV. Distortion of Curvature. Engl. Mech., XXXVIII. (1884) p. 497 (1 fig.). V. Summary of Formula-On Further Approximations for the Distortion, and General Remarks-Proposed Eye-piece. The first lens plano-concave, the second plano-convex, with focal length numerically equal to that of the first, and placed at a distance from it equal to twice the focal length of the eye-lens, the curved side of each of

« SebelumnyaLanjutkan »