PRACTICAL TREATISE 



ON THE DSE OF 



ERRATA. 



Instead of Table, page 466, read the following, viz. 



Object 

 Glasses, 



1 

 1 



i 



i 

 k 



Angular 

 Aperture. 



2 inches 12 degrees 



15 



22 



57 



75 



105 



108 



150 



Magnifying Powers with the various 

 Eye- Glasses. 



6C 

 12C 



33 



220 

 620 



1200 

 2000 



A.D, 65, writes that small and indistifroroujects DeconrerKO^r- 

 and more distinct in form when seen through a globe of glass 

 filled with water.* Pliny, who died in a.d. 79, mentions 



* " Literse quamvis minuts et obscurse, per vitream pilam aquS plenam, 

 majores clarioresque cernuntur." — Nat. Qiioest, lib. i., cap. 7. 

 1 



