OBJKCT GLASSES. 105 



The writer has before Jiim a glass of the latter angle, 

 '(115,) made by C. A. Spencer & Sons. It is what 

 they call one of their " professional series" a dry one- 

 fourth ; the makers ought not to expect that this glass 

 should be called on for work requiring oblique pencils 

 greater than 100. 



Now this glass this professional one-fourth will 

 give me real good shows, even when worked at all the 

 obliquity obtainable on my Zentmayer stand; and thus 

 have I seen with it the longitudinal markings on the 

 balsamed surriella of the Moller test-plate, and this is a 

 test that will defeat many dry eighths, engraved by 

 their makers as having 160 or more angle. 



From this little experiment one that the writer has 

 repeated scores of times in the interests of his friends 

 :some curious conclusions might be arrived at, which, 

 although possibly coherent and plausible in detail, 

 become absurd when considered collectively; thus it 

 misfht be held : 



r^ 



First. That both glasses having at least 160 of aper- 

 ture, are in fact high-angled glasses. 



Second. That of the two named, the Spencer is the 

 better glass. 



Third. That the Spencer objective has realty but 

 an angle of 115, as marked by its maker; that its capa- 

 bility of admitting working beams up to 140 gives it 

 no real claim to those figures. 



Fourth. That, as any good eighth of 140 will 

 -easily show the longitudinal markings of the surriella, 

 it is proven that the one referred to has not that angle 



