170 THE MICROSCOPE. [August, 



slides and especially adapted to photomicrography, and their 

 apochromatic homogeneous immersion condenser, of n. a. 1.40, 

 for special researches. The Abbe condenser, now made also in 

 an achromatic form by its original producers, the Zeiss house, is 

 universally adopted by the continental makers. 



The only special exhibits in illumination worth mentioning 

 were in the use of electricity. Dr. H. Van Heurck, for ten years 

 an enthusiastic advocate of this method, exhibited the various de- 

 vices he has employed. He believes that the incandescent light, 

 while possessing the mildness of the petroleum lamp, excels it 

 and nearly equals monochromatic sunlight in the power of show- 

 ing with clearness fine details like the markings oi Amphipleura 

 or the 19th band of Nobert's plate. This is believed to be due to 

 its o-reatcr intensitv. enablinsf sufficient lio-ht to be obtained from 

 a very small pencil of rays, and to the greater proportion of the 

 shorter waves of the blue and violet end of the spectrum, which 

 gives its peculiar whiteness to this light. In view of these ad- 

 vantages it is to be regretted that this light, though perfectly at- 

 tainable with the now available apparatus, has not yet been able 

 to compete successfully, for general use, w^ith the more convenient 

 petroleum lamps. 



A remarkable collection of batteries, dynamos, and lights suit- 

 able for microscopical use was exhil:>ited by the great French 

 electrician, G. Trouve, of Paris. His "• photophore," consisting 

 of a little drum containing a bull's-eye lens with a tiny electric 

 loop behind it, the whole sliding easily up or down a vertical 

 pillar and capable of turning at any angle, like the search-light of 

 a ship, seems by far the best electrical illuminator yet produced. 

 It apparently needs only to be freed from its dependence on the 

 necessarily troublesome battery by the presence of an electric 

 service-wire in everv house to become the illuminator of the mi- 

 croscope. By this exhibit. M. Trouve, whose biography, lately 

 published in a fascinating book as ••' The History of an Inventor," 

 seems more like a romance than a history, added another diploma 

 of honor to a former list of awards of which an}^ inventor in any 

 line of research might well be proud. 



Photomicrography. 



This class was, of course, exceptionally prominent. The appa- 

 ratus pertaining to it was mostly included in the makers' exhibits 

 of microscopes and accessories. 



A. Nachet, of Paris, whose personal experience in photomicrog- 

 raphy insures a special interest in the work and an exceptional 

 familiarity with its demands, was first in the variety of his appli- 

 ances and unsurpassed in their quality and completeness. His 

 " grand apparatus" has a horizontal bellows capable of easy ad- 

 justment for distances up to about two meters. The stand is 



