444 Eisen: A successful achromatic light-filter. XIV. 4. 



Auch die Firma Zambelli cc C<>. in Turin liefert nach meinen 

 Angaben eine solche Badevorrichtung , in der aber die Gummiringe 

 durch einige Klammern ersetzt sind, welche ihrerseits an dem Deckel 

 lixirt wurden. Die Klammern haben auch zugleich das Gute, dass 

 sie das Hineinfallen der Objectträger verhindern. 



Ich finde diese Veränderung sehr praktisch, da sie die Behand- 

 lung, welcher die Objectträger zu unterwerfen sind, sehr vereinfacht. 



[Eingegangen am 14. December 1897.] 



A successful achromatic light-filter for high power 



microscopic work. 



By 

 Gustav Eisen, Ph. D., 



Curator California Academy of Science, San Francisco, Cal., U. S. A. 



Owing to the erection of a tall building in front of my labora- 

 tory, and to the cousequent shutting off of much ot the white-cloud 

 light, 1 was forced to experiment with artiticial lights for high power 

 work. For a long time my efforts were unsuccessful, and I was 

 obliged to remove to other quarters ; but these proved also unsatis- 

 factory as far as the cloud light was concerned, and the latter part 

 of last year, I again took up my experiments. It is not necessary 

 to record here the many failures , and I will simply statt- that I 

 used every stain and liquid that could suggest itself, beginning 



with copper Solutions of varying strength , and ending with aniline 

 colors of different tints. Finally a combination was found, which, 

 in my opinion , is not only a Substitute for the best white-cloud 

 light, but is as much superior to it as an apochromatic lens-system 

 is superior ^o an ordinary one. This light is not only more brilliant 

 than cloud light, but is much softer to the eyes and possesses also 

 the good quality of being steady. Whereas formerly I could work 

 only three or four hours with good daylight, with the artiticial light 

 1 can uow easily work from eight to ten hours, without injury to 

 the eyes and without tiring. 



