1070 SUMMARY OF CURRENT RESEARCHES RELATING TO 



By this arrangement any given metal can be used, not merely in 

 conjunction with platinum only, as before, but also with any other 

 metal. 



A simpler and cheaper form is also supplied, in which the discs 

 are replaced by two supports, each carrying a single arm for the 

 electrodes. 



Optical Arrangements for Photo-micrography, and Remarks 

 on Magnification.* — Mr. E. Hitchcock discusses the relative merits 

 of the two methods of obtaining amplification in photographing 

 microscopic objects : viz. by regulating the distance of the sensitive 

 plate, or by the interposition of an eye-piece, or a supplementary 

 lens, usually an achromatic concave, between the objective and the 

 sensitive plate. The following are his conclusions : — 



" Summing up this matter, we are personally inclined to favour 

 the use of large plates, 8 by 10 in. for example, using the lens with 

 an amplifier instead of an eye-piece, for the reason that large pictures 

 highly magnified can thus be obtained of exquisite definition. These 

 will bear further enlarging with the solar camera. There remains, 

 however, the consideration of expense, and the inconvenience of using 

 such a large apparatus under ordinary circumstances. It is, unques- 

 tionably, more convenient in most cases, to use smaller plates and to 

 work wdth an eye-piece. Still better, to use an amplifier in place of the 

 ocular, for then it is possible to attach the amplifier to the camera in 

 such a position that when the object is focused with the eye-piece it 

 is also in focus on the ground glass of the camera when the latter is 

 attached. With such an arrangement, a quarter-plate camera can be 

 used with perfect satisfaction, giving negatives equal to any that can 

 be made. 



The same cannot be said when the ocular is used, although there 

 is no doubt thoroughly satisfactory results can be obtained with the 

 ocular on small plates." 



Actinic and Visual Foci in Photo-micrography with High 

 Powers.f — It is very commonly said that whilst the diflerence between 

 the visual and the actinic focus is considerable when making photo- 

 micrographs with low powers, it is not appreciable when using high 



* Araer. Mon. Micr. Joiirn., vi. (1885) pp. 168-70. 



+ Ibid., pp. 193-5, (Paper read before the American Society of Microscopists.) 



