70 SUMMARY OF CURRENT RESEARCHES RELATING TO 



a layer of felt B, approximately 2 in. in thickness. Tins felt layer is in 

 effect a shock absorber. The felt in turn is supported by the fiat top of 

 the movable table C. This table may be equipped with cupboards and 

 drawers giving the necessary space for the special equipment for the 

 various kinds of photomicrography which may be attempted. At the 

 corners of the table near the wheels, where castors are placed, there are 

 also placed spring checks D, which can be adjusted to press against the 

 floor and tlius prevent any undue freedom of movement of the table 

 while it is in use. Examples of six-minute exposures, at 1000 magnifi- 

 cation, are extremely fine. 



; (5") Microscopical Optics and Manipulation. 



Optic Projection by S. H. and H. P. Gage.* — This book is a very 

 complete and up to date exposition of its subject. The authors' intention 

 is not only to give an explanation of the principles underlying the art, 

 but to give such simple and explicit directions that any intelligent 

 person can succeed in all the fields of projection. At the same time 

 attention is devoted to the physiological principles of vision, so that the 

 investigator in novel or special applications of projection may have a 

 clear idea of the methods which must be adopted to obtain success. 

 While impressed with the general excellence of the apparatus supplied 

 by many different makers, the authors point out certain general defects, 

 among them being an uncertainty as to the right and the wrong way of 

 using the auxiliary parts of an apparatus. The authors think that 

 manufacturers should give attention to this point, and should construct 

 their apparatus so that it can be used in only one, and that the right 

 way. Thus, to take a simple example, the condenser is usually so 

 mounted that it may be used with either end facing the arc lamp : this 

 ought to be impossible, and could be easily obviated. This idea oi 

 rendering the apparatus as far as possible " fool-proof " is a strong 

 feature of the book. Every chapter is followed by a summary of useful 

 instructions, entitled " Do " and " Bo not," with the intention of re- 

 ducing the difficulties of operators. 



The work is divided into fifteen chapters, the first six of which deal 

 with the magic-lantern as operated with different kinds of light (direct 

 current, alternating current, house electric light, lime-light, ordinary 

 lamps, and sunlight). Other chapters deal with projection of opaque 

 objects, lantern slides, the projection Microscope, drawing and photo- 

 graphy with projection apparatus, moving pictures. Chapter xn is a 

 useful discussion of projection rooms and screens. Chapters xiii and x i v 

 treat of electric currents and their measurements, and optics of pro- 

 jection ; and Chapter xv discusses normal and defective vision. An 

 appendix gives a brief historical statement on the origin and development 

 of projection apparatus. There are modern and historical bibliographies 

 and a list of manufacturers of projection apparatus. 



* Comstock Publishing Co., Ithaca, New York (1914) 731 pp. (413 figs.). 



