668 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
use of objective No. 7. The instrument is provided, like the others, with 
means for fixing the stage, polarizer and analysers, arrangements tor 
convergent and parallel light, Bertrand lens, objective clamp, &c. 
Model No VI. (fig- 71) is in size and construction precisely similar 
to model No.' II., but differs from it and the other instruments by a 
