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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. 



. 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, 



