146 THE MICKOSCOPE. [July, 



Referring particularly to the catalogue of the Bausch and Lomb 

 Optical Co., we will state the purpose for which they were in- 

 tended. 



Biological. — Laboratory, student, and professional use. 



Large Biological. — Advanced laboratory, student, and profes- 

 sional use. 



Harvard. — Laboratory, student, and professional use. 



Model. — Laboratory, student, professional, and amateur use. 



Physican. — Professional. 



Investigator. — Student, professional, and amateur use. 



U^iiversal. — Student, professional, and amateur use. 



Concentric. — Professional and amateur use. 



Professional. — Advanced laboratory, professional and ama- 

 teur use. 



For ordinary professional use, including urinary examinations, 

 the f -inch 27 degrees and ^-inch no degrees objectives w^ill 

 be found sufficient. For bacteriological examinations a higher 

 power, such as a i-i 3-inch homogeneous immersion objective will 

 be necessary. If means will permit, an investment in the |-inch 40 

 degreesand i-^-inch i3odegrees, or f-inch40 degrees and T-6-inch 

 140 degrees will be well applied. This latter is in very general 

 use and may be very highly recommended. In botanical work a 

 lower power than those mentioned, such as a 2-inch 13 degrees 

 or preferably, 2-inch 15 degrees will be necessary. For ama- 

 teur use the ordinary outfit of J inch 27 degrees and 1-5-inch no 

 degrees, with the addition of a 2-inch, preferably of the better 

 grades, will do. If the examination of diatoms will be followed, 

 the i-6-inch, 140 degrees and i-i 2-inch homogeneous immersion 

 will probably be required. For the student, the |^-inch 28 degrees 

 and i-6-inch 116 degrees, or |-inch 27 degrees and i-6-inch no 

 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 every-day work does not require 

 this maximum of optical results, and can be accomplished com- 

 pletely and with comfort with objectives of comparatively low 

 aperture. Some years ago microscopists were divided into two 

 classes, the new school of wide aperture and the old school of 

 narrow aperture. The state of affairs existing then has happily 

 changed, concessions having been gradually made, so that now 

 the advantages of both class of objectives are a^opreciated and there 

 are few microscopists of standing who would recommend only one 

 or the other kind. 



In these days of competition, prices alone are too often made 

 the object of inducement, without any reference to quality. Be 

 distrustful of all such objectives, and if contemplating their pur- 



