96 



If means will permit, an investment in the f inch 

 40 degrees and -|- inch 130 degrees, or f- inch 40 de- 

 gress and i inch 140 degrees, will be well applied. 

 This latter is in very general use and may be highly 

 recommended. 



In botanical work a lower power than those men- 

 tioned, such as a -2 inch 12 degrees or, preferably, 2 

 inch 15 degrees, will be necessary. 



For amateur- use the ordinary outfit of } inch 27 

 degrees and -J- inch 110 degrees with the addition of 

 a 2 inch, preferably of the better grades, will do. If 

 the examination of diatoms will be followecf, the -J- 

 inch 140 degrees and T 1 2 inch homogeneous immer- 

 sion, will probably be required. 



For the student, the f inch 28 degrees and inch 

 110 degrees, or f inch 27 degrees and -J- inch 110 

 degrees objectives, will ordinarily be ample. 



Although from an optical standpoint it is true that 

 objectives give more detail as they increase in their 

 angular apertures, it will have been seen that the 

 highest class of objectives is not always recommended. 

 A great portion of everyday work does not require 

 this maximum of optical results, and can be accom- 

 plished completely and with comfort with objectives 

 of comparatively low aperture. Some years ago micro- 

 scopists were divided into two classes, the new school 

 of wide aperture, and the old school of narrow aper- 

 ture. The state of affairs existing then has happily 

 changed, concessions having been gradually made, so 

 that now the advantages of both classes of objectives 



