1892.] MICROSCOPICAL JOITIINAL. 157 



the capabilities of the process. For the representation of very 

 delicate work, the numerous photo-gelatine processes are more 

 satisfactory, as the minutest detail can be accurately shown, but 

 thev are much more expensive, and must be printed on special 

 paper and presses. But grapliic illustrations in some form add 

 largely to the attractiveness of an article, as well as enabling the 

 reader to comprehend at a glance the idea which is sought to be 

 conveyed. Few can draw, but dry plates have made photo-microg- 

 raphy almost a pastime, and the half-tone process oHers, by all 

 odds, the best mode of reproducing photographs with all the ac- 

 curacy of the original, and with a minimum of expenditure of time 

 and money, and it is to be hoped scientific periodicals will be led 

 to make more use of this new method. 



Impressions of the Aiitwerp Microscopical Exposition. 



By R. H. ward, M. D. 



President's Remarks at the Microscopical Section of the Troy, N. Y., Scientific Association, 



Oct. 19, 1 89 1. 



{^Continued from page 140.] 



Illuminating Apparatus. 



Though made a separate class in the official announcement of 

 the exposition, most of the illuminating expedients were neces- 

 sarily merged in the exhibits already mentioned. The recent re- 

 markable development of the substage condenser, as an inevitable 

 result of the adoption of the apochromatic objective, was seen 

 everywhere. Powell & Lealand submitted their dry apochro- 

 matic condenser of n. a. 0.95, able to work through common 

 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 of Amphiplcura 

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

 its greater intensity, enabling sufficient light 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, with the more convenient 

 petroleum lamps. 



