296 SUMMARY OF CURRENT RESEARCHES RELATING TO 



object with a magnification of not moro than 100 diameters, and after- 

 wards reproducing it magnified fivo times so as to obtain a photograph 

 magnified 500 diameters proper for photo-printing. Fine details aro 

 thus brought out, invisible to the naked eye in the smaller photograph. 



Crystal Palace Photographic Exhibition. 



[Special Certificate in Class F. (General Appliances and Plant) " awarded to 

 James Swift & Son for Apparatus and Microscopes arranged for Photo- 

 micrography."] 



Journ. and Trans. Phot. Soc. Or. Britain, XII. (1888) p. 80. 



Jeserich, P. — Die Mikrophotographie auf Bromsilbergelatine bei natiirlichem 



una kiinstlichem Lichte unter ganz besonderer Berucksichtigung des Kalk- 



lichtes. (Photomicrography by the bromo-silver gelatin process with natural 



and artificial li^ht, with special reference to the limelight.) 



xiv. and 24G pp. (4 photomicrographs and (JO figs.), 8vo, Berlin, 1888. 

 Knosel's Photomicrographs. 



[Note on some photomicrographs of animals and plants, taken by the oxy- 

 hydrogen light.] 



Zeitschr. f. Naturwiss., LX. (1887) p. 481. 



(5) Microscopical Optics and Manipulation. 



Advantages of a Knowledge of the Theory of the Microscope. — 

 Dr. W. H. Dallinger writing * on the Euglish translation of Niigeli and 

 Schwendener's ' The Microscope in Theory and Practice,' says that it 

 " opens to English readers an entirely new page in microscopical litera- 

 ture. It leads the way in supplying a want which every thorough micro- 

 scopist has realized for the last twenty years. In a complete form this 

 treatise has been accessible to the German roader for at least ten years. 

 The absence of it, or an equivalent, in the English language has been a 

 most serious drawback to the advancement of the highest optical work in 

 English Microscopes. In optical manipulation, the English optician at 

 his best proves not only equal to any in the world, but in the highest 

 class of work, has shown lately that he takes a foremost place. But 

 with no attempt on the part of English mathematicians and microscopists 

 to become masters and expounders of the theory of the Microscopo and 

 of microscopic vision, the practical optician can make no real advance. 

 English " stands," and those made in America on English models, are of 

 exquisite construction, and are quito equal to our present necessities ; 

 but for all the great advances and improvements that have been made in 

 English object-glasses during the last fifteen years, wo are, for all practical 

 purposes, primarily indebted to Germany. And this is readily explained 

 by the fact that the German specialists have made a systematic and per- 

 sistent study of the theory of the Microscope. 



" It is not forgotten that it was to the suggestion of Mr. J. W. 

 Stephenson that we are indebted for the invaluable improvements that 

 belong to the homogeneous system of lenses.f But, without doubt, it 

 was on account of the insight which a study of the theory of microscopic 

 vision brought with it, that Mr. Stephenson perceived at onco the 

 advantages of great numerical aperture, and the new way to obtain it. 

 Moreover, it is certain that Prof. Abbe was approaching this very 

 method of employing lenses, though from another point, and not in so 

 direct a way. It would have been shortly reached by him, there can be 

 but little question ; but when it was reached, what did a constant, 

 enthusiastic, and laborious study of the theory of the Microscopo carry 



* Nature, xxxvii. (1887) pp. 171-2. f See this Journal, 1878, p. 51. 



