I9IS-] 



MARSHALL-BANKS— NEW NEPHELOMETER. 



181 



neutral tinted glass H. This adjustment is made by the thumb- 

 screw / and the position of the wedge is read on a scale mounted 

 alongside (not shown in the diagram). A compensating wedge 

 wedge may be placed at J,h\xi unless the sliding wedge //is of fairly 

 steep pitch, this is unnecessary, as the illumination of the field is 

 sufficiently uniform without it. All parts of the instrument from 

 which extraneous light may be reflected are painted a dead black. 



Fig. 2. 



The construction of this instrument was delayed owing to diffi- 

 culties encountered in securing neutral tinted glass. While await- 

 ing its completion we decided to improvise a nephelometer in which 

 several minor changes have been made. Among these may be men- 

 tioned the substitution for the glass wedge of a metal plate in which 

 was cut a tapered slot. With this instrument we undertook some 



