Class X.] MICROSCOPES—RATIOS OF TIIEIR MAGNIFYING TOWERS, BY LEONARD. 267

worked into convex spherical surfaces, is also worthy of •notice. The Jury considered Mr. King as well deservingHonourable ’Mention.

Pritchard (No. 248, p. 435) exhibits an old-fashionedachromatic microscope, with indifferent object-glasses.The working of the mechanical parts is very good. Thisform of instrument is that which led the way in the greatadvance that has been made in the microscope by theintroduction of achromatic object-glasses. The Juryvoted Honourable Mention to Mr. Pritchard.

Ladd (No. 291a, p. 440) exhibits a microscope fur-nished with chain and spindle movements, in place ofrack and pinion. This movement has been applied to themicroscope many years since, by Mr. Julius Page. Themotion is smooth, and totally free from loss of time, andis likely to stand well the effects of constant use. TheJury award Honourable Mention to Mr. Ladd.

Pilliscuer (No. 269, p. 437) exhibits a large micro-scope stand, which is good for its price, but unnecessarilylarge and inconvenient for use. He also exhibits twosmall microscopes.

Jackson, E. and W. (No. 258, p. 436) exhibit plain andexcavated slips of glass, sections of tubes of various forms,for the construction of cells for mounting wet prepara-tions, and thin glass for covering them, of various thick-nesses. These materials are exceedingly useful forscientific microscopists.

Hudson (No. 256, p. 436) exhibits microscopic objectsintended for the use of the medical student, physiologist,and naturalist.

Hett (No. 249, p. 435) exhibits a variety of admirably-injected microscopic objects, illustrating the utility of themicroscope to the physiologist. A Prize Medal wasawarded to Mr. Ilctt.

Poulton (No. 252, p. 435) exhibits some well-executedmicroscopic objects, with drawings to illustrate theirstructure.

Stark (No. 234, p. 438) exhibits microscopic objects,mounted in (jutta percha cells, instead of glass; and alsoslides for exhibiting opaque objects.

Sharp (No. 308, p. 442) exhibits a set of high powerlenses, ten in number, for a microscope from one-tenth toone-hundredth of an inch focal length.

Shadbolt (No. 677a, p. 469*) exhibits a sphero-annularcondenser, for concentrating light on transparent objectswhile under microscopic examination, the object alonebeing illumiuated whilst the field of view is dark. APrize Medal was awarded to Mr. Shadbolt.

The principle of this condenser was suggested by Mr.J. F. Wenham, of Brixton, in his parabolic condenser.Mr. Shadbolt’s condenser carries out Mr. Wenham’s prin-ciple, with the advantage of superior reflecting arrange-ments, greater facilities of construction, and less liabilityof derangement.

Other microscopes are exhibited by Field and Son(No. 250, p. 435), Elliott and Sons (No. 320, p. 443),Watkins and Hill (No. 659, p. 466*), Abraham (No.263, p. 436), Griffin (No. 457, p. 463); but they are notsuch as demand especial notice.

Let us now turn our attention to the microscopes ex-hibited by France; and first in order is Natchet (France ,No. 1370, p. 1242). The object-glasses, though inferiorto both those of Ross, and Smith and Beck, are by farthe best of the foreign ones. They vary from a focus ofone inch to that of one-eighteenth of an inch. Thefollowing were examined; that with—

Ath of an inch focal length, has an aperture of 134 D .

|th „ „ 108 3 .

Jth „ „ 88 3 .

In all of them the spherical aberration is not corrected;and although the method of adjusting by the separationof the lenses, invented by Ross, is adopted, vet the systemis such that they are not correct at any distance. Theworkmanship of the stand is very good; and there aretwo ingenious forms of microscopes exhibited. One hasthe object-glass below the stage, with the tube inclinedat a convenient angle and a reflecting prism for theexamination of chemicals, or for dissecting transparentobjects under fluids. The other is a dissecting micro-

scope, with the body inclined in a convenient direction,and the image erected by reflecting prisms, so as to enablean observer to look in a convenient position whilst dis-secting an object in fluid, which must be kept horizontal.A Prize Medal was awarded to M. Natchet.

Some microscopes, excellent for their price, are ex-hibited by Bernard (France , No. 762, p. 1217). Theseinstruments are the cheapest in the Exhibition, thoughnone are of the first order. Honourable Mention isawarded to M. Bernard.

Chevalier (France , No. 1729, p. 1259) exhibits amicroscope, with indifferent object-glasses. The work-manship of the mechanical part, however, is very good,the mode of mounting is excellent, and the instrument isconvenient for all kinds of microscopic observations. TheJury voted Honourable Mention to M. Chevalier.

Some excellent microscopes, for their price, were alsoexhibited by Buron (France, No. 443, p. 1199).

Merz (Bavaria , No. 30, p. 1100 ) exhibits a microscope,the mechanical parts of which are beautifully executed.The object-glasses are of small aperture, and the sphericalaberration is not corrected. The ouc-twelfth of an inchfocus has an aperture of only C5 3 , and the one-eighth ofan inch that of 55° only.

IIazart (America , No. 1C, p. 1433) exhibits a largeinstrument, furnished with very deep Huygenian eye-pieces, giving the usual extensive field obtained by such;it has, besides, two convex lenses in the body for enlarg-ing the field of view. Neither chromatic nor sphericalaberration is properly corrected, and the workmanship isnot good.

Pick (Russia, No. 170, p. 1372) also exhibits a micro-scope, but it is an indifferent instrument.

We will now speak of some of the uses of the beautifulinstruments we have just described; the most importantillustration of their utility in the Exhibition is shown byLeonard (No. 306, p. 442), in his correct representationof many different substances, Ac., when highly magnified.He has selected several articles of food in daily use, alsothe substances with which they are sometimes adulterated,&c., as in the subjoined list.

Frame 1.

1. Transverse section of raw coffee berry, magnified16 diameters.

2. Thin section of raw coffee berry, showing globulesof essential oil, magnified 250 diameters.

3. Investing membrane, magnified 250 diameters.

4. Transverse section of chicory root, magnified 250diameters.

5. Longitudinal section of chicory root, central fibres,magnified 250 diameters.

6. Longitudinal section of wheat grain, showing theembryo.

7. Wheat starch, magnified 250 diameters.

8. Investing membrane, 250 diameters.

9. Maize , longitudinal section, showing the embryo,magnified 12 diameters.

10. Maize starch, magnified 250 diameters.

11. Investing membrane, magnified 250 diameters.

Frame 2.

1. Horse-bean, transverse section, magnified 25 dia-meters.

2. Horse-bean, starch globules, magnified 500 dia-meters.

3. Horse-bean, investing membrane, magnified 500diameters.

4. Potato starch, magnified 500 diameters.

5. West India arrow-root, magnified 500 diameters.

6. Sago meal, magnified 500 diameters.

7. Rice (raw ■, magnified 500 diameters.

8. Rice (boiled), magnified 500 diameters.

Frame 3.

1. Healthy nurse’s milk, magnified 1,200 diameters.

2. Pure cow’s milk, magnified 1,200 diameters.

3. Cream of cow’s milk, magnified 1,200 diameters.

4. Curd of cow’s milk, magnified 1,200 diameters.