32 
REVIEWS. 
his operations are conducted, to a certain degree, depends on “ the build” 
and finish of his instrument. French object-glasses, of very good defining 
powers, may be obtained ; but they are not equal to those furnished by the 
best English makers. 
Fig. 4. 
Within the last few years considerable advances have been made in 
grinding object-glasses, whose perfection is now estimated by the accuracy 
with which minute pores, striae, or other markings on certain objects which, 
