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MARSHALL-BANKS— NEW NEPHELOMETER. [April 23, 



Briefly the design of the instrument is as follows : The suspen- 

 sions to be compared are contained in the two cells A and B shown in 

 the accompanying diagram (Figs, i and 2). These consist of cylin- 

 drical glass tubes about 4 cm. high and i cm. in diameter. A glass 

 plate is sealed into one end, while the other end is covered by a cir- 

 cular plate of glass slightly countersunk and held in place by caps 

 of black fiber. These prevent stray light reflected from the edges 



DIAGRAMMATIC -REPRESENTATION 

 OF FIELD 



LIGHT FROM TUBE A = HORIZONTAL SHADING ! 



LIGHT FROM TUBE B= VERTICAL SHADING 



w////////////w//mm^//^^^^^^ 



Fig. I. 



of the glass from entering the instrument. Difficulties arising 

 from the agitation of the liquid by plungers are also thus avoided 

 by having the cells completely enclosed. The cells rest on a shelf 

 and are illuminated normal to their axes by a parallel beam of light 

 from a 100 Watt lamp. The rays reflected from the suspended 

 particles pass upward to the two mirrors E and F whence they are 

 reflected into the magnifying eyepiece G. This is focused on mir- 

 ror E. A circle cut through the silvering of mirror E permits the 

 juxtaposition of the light from tubes A and B thus giving the eye- 

 piece a field which is represented diagrammatically in the accom- 

 panying illustration. Photometric balance is effected by changing the 

 intensity of the light from tube B by means of the sliding wedge of 



