422 SUMMARY OF CUEKENT EESEARCHES RELATING TO 



serviceable for the measurement of liquids of refractive index as high 

 as 1*70 by replacing the crown illuminating prism by a suitable dense 

 flint prism. In using the refraetometer for solid and plastic bodies it 

 would be more convenient if the prism box were designed to open away 

 from the operator. 



C4) PhotomicrogrrapJby. 



Exposure in Photomicrography.*— F. C. Lambert has compiled 

 three tallies which are intended to afford means of scientifically calcu- 

 lating the exposure required wlien any of the essential factors (hght 

 source, object, objective, plate) are varied. The tables are too elaborate 

 for reproduction, Imt they, as well as the subsequent discussion at the 

 Eoyal Photographic Society, should be read by those interested in the 

 subject. 



(6) Miscellaneous. 



" The Microscope." f— The twelfth edition of this valuable work, by 

 S. H. Gage, has now been published, and the contents of the present 

 editions have been thoroughly revised. In his preface the author 

 appeals to the comparison of manufacturers' ten-year old and modern 

 catalogues for a realization of the advances in microscopy during recent 

 years. Although nothing fundamentally new has appeared within the 

 last ten years, yet many processes have been made applicable and much 

 apparatus has been rendered really serviceable. Among the most im- 

 portant developments, especially for students of biology, the author 

 reckons the following : — 1. The single objective binocular for all 

 powers of the Microscope from the lowest to the highest. 2. The 

 dark field illuminated for all powers, especially the highest, with which 

 the finest details in living structures can be seen with marvellous clear- 

 ness. This makes it possible to compare the hving cell with the fixed 

 and stained one. 3. The perfection of apparatus with which the power- 

 ful electric lights recently produced have become available for demon- 

 strations and for drawing with the projection Microscope. 4. The per- 

 fection of photographic light filters, and the production of dryplates, 

 sensitive to the whole spectrum, make it possible to get good photo- 

 graphs of any microscopic specimen, and indeed of any specimen. 

 5. From the numbers who are affected, and the extent of its application, 

 perhaps the greatest improvement of all has been the production of a 

 glass filter, which, when used with a gas-filled Mazda lamp, gives a light 

 of true daylight quality, and of sufficient intensity for all powers of the 

 Microscope. 



The author endeavours to render the microscopist thoroughly master 

 of the principles and manipulations, and he spares no pains, by descrip- 

 tions and figures, to attain this object. The recent improvements are 

 treated with especial care. He omits the pages relating to micro- 



* Photographic Journal, Ivii. (June 1917) pp. 205-15 (5 figs.). 



+ The Microscope : an Introduction to Microscopic Methods and to Histology, 

 by Simon Henry Gage. Ithaca, N.Y. : Comstock Publishing Company, 1917. 

 ix. and 472 pp. (252 figs.). 



