720 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Microscopes which, like Eoss's newest pattern, have the fine 

 adjustment separate from the main tube, and in which the stage can 

 he swung to any angle, or removed altogether by simply loosening a 

 screw, are especially adapted for the above fitting, since the upper 

 lens-system can be as large in diameter as the main tube. 



The lenses I used were the ordinary ' spectacle ' lenses, including 

 a pair of hemispheres, and the field is nearly as great as that of Hoff- 

 mann's instrument, just taking in the two axes of Brazilian topaz. 



With such an arrangement, combined with the selenite stage, 

 nearly or quite all the beautiful experiments given in Dr. Spottis- 

 woode's little treatise on ' Polarized Light,' can be made. 



It is more than a dozen years since I made the above addition to 

 my Microscope ; and I am surprised that Norremberg's lenses are not 

 included among the usual ' accessories ' of (at any rate) first-class 

 Microscopes." 



Sternberg's * Photomicrographs and how to make them.' — 

 Dr. G. M. Sternberg, Surgeon-Major U.S.A., has just published a 

 work entitled ' Photomicrographs and how to make them,' with illus- 

 trations of microscopic subjects, printed by the Boston Heliotype 

 Printing Company from his original negatives. 



The subject is dealt with carefully, and the prints afford evidence 

 of the value of the method employed, which differs somewhat from 

 that generally used in this country. He largely advocates for low 

 powers the use of light reflected from a blue sky, and giving long ex- 

 posures, the apparatus being a little elevated from the usual horizontal 

 position. With high powers, Dr. Sternberg advises direct sunlight, 

 the employment of a heliostat, ammonio-sulphate of copper cell, long 

 focus condensing lens, and substage achromatic condenser. His arrange- 

 ment for these, and the position of the focusing screen, when using 

 a room as a camera, are not quite the same as are commonly adopted. 

 Some of the figures clearly show that, with a proper selection of 

 objects and this mode of taking the negatives, photomicrography can 

 render very useful service to the microscopist. There is one plate, 

 No. xii. (the fourth square of one of Moller's type-plates of the 

 Diatomaccfe), which is a marvel of excellence, considering the diffi- 

 culty of the subject, the photograph being made by a Powell and 

 Lealand's 1-2 in. objective. There is also an admirable figure, 

 pi. xvi., of Navicula lyra, taken with a Zeiss l-6th dry objective, and 

 ToUes' amplifier, the heliostat being used. Full directions are given 

 for the use of the apparatus and development of the plates. Dr. 

 Sternberg, to render the work more useful, has selected a series of 

 objects, and has given explanations, so as to carry the student forward 

 in his studies by what may be called " elementary lessons in biology," 

 passing from Amoeba to bacteria, unicellular algse, epithelium and 

 other scales, blood-globules, pollen, epidermis, hairs and woody tissue 

 of plants, diatoms, adipose tissue, sarcoma and insect parasites, &c. 

 One figure is given illustrating the gi-eat difference in the appearance 

 of the print from a negative of a diatom illuminated by direct light, 

 and by the use of the " spot-lens," much greater solidity being given 

 by the latter, though unfortunately with less detail. There is also a 



