•THEAlCR^iSCOpE 



AOIflMLw^A(2^zINE . 



Vol. XII. 



WASHINGTON, D. C, JULY, 1892. 



No. 7. 



Selecting a Microscope. 



By EDWARD BAUSCH, 



ROCHESTER, N. Y. 



S^Cofitiiiued from page /J/.] 



Objectives and Eye-Pieces. — It is hoped that the information 

 givenof the various qualities in an objective will aid to make a suit- 

 able selection of the optical parts. As stands have been classified in 

 long and short standard tubes, the next thing to look for after the 

 stand has been selected is the adaptability of objectives and eye- 

 j^ieces to it. 



As will have been seen under the proper head, a variety of 

 powers is obtained by a suitable combination of eye-pieces and 

 objectives ; and while power alone can be obtained bv increasing 

 the power of the eye-piece, it is not advantageous to do so. For 

 ordinary work no higher eye-piece than a J should be used. In 

 catalogues, many outfits are made up of one eye-piece and two 

 objectives, but this is only for the purpose of reducing price to a 

 minimum. It is always advisable, when means will permit, to select 

 two eye-pieces, preferably the 3-inch and i -inch, and insist that they 

 be par-focal, as this will be found extremely convenient and will 

 not disturb the optical standard length. If for any work ^inch 

 or higher powers are desired, the solid eye-piece may be recom- 

 mended. The periscopic are advantageous for micrometric tests 

 and other w^ork where a large or flat field is desirable. 



For students' and practitioners' use, the outfits as made up in 

 catalogues are usually sufficient, except as above recommended, 

 where but one eye-piece is given ; it is well to select two v/here 

 means will permit. 



