192 THE AMERICAN MONTHLY [Nov 



diameters; Pleurosigma with 2-3 inch objective ; Pleuro- 

 sigma magnified 450 diameters ; Same, 1450 diameters; 

 same, 6,000 diameters ; same 10,000 diameters and same 

 360,000 diameters showing part of the lattice-work open- 

 ing made by a sixth objective focussed on a sixth. 



Description of the apparatus is as follows : "Upon the 

 extreme left of the picture, and under the table are 

 three resistance coils used to regulate the five-hundred 

 volt alternating current with which my laboratory is 

 supplied, so as to reduce it suitably for the arc lamp, 

 shown at the extreme left upon the table. Next to the 

 right are the condensing lenses, and then the alum filter 

 with its bellows, and after that the lenses used to render 

 the rays parallel. The revolving diaphragm is placed at 

 the right hand end of the parallelizing lenses. Between 

 the bellows of the filter-cell and the parallelizing lenses 

 there is a screen holder, in which I place stained gelatin 

 films to screen out such rays as may not be desirable. 

 Beyond the revolving diaphragm the light next enters 

 the sub-stage Abbe condenser and thence through 

 the microscopic slide to the two microscopes and camera. 

 The light is about 2,000 candle power and the results are 

 extremely satisfactory. 



In a slightly modified form of the same apparatus, the 

 two microscopes are provided with tripple nose-pieces 

 and projection lenses. 



The complete form of the instrument now being manu- 

 factured, will consist of a solid brass bed-plate long 

 enough to hold the entire system of apparatus, with 

 means for adjusting tlie various parts from the rear of 

 the camera. The entire system will be enclosed in a box 

 capable of screening out all actinic rays. Dust and 

 aqueous vapor particles will be removed from the interior 

 of the instrument by a special device which need not here 

 be described. I am having made a similar outfit from 

 which I will have eliminated all the lenses which have 



