322 The Microscope. 



ment to myself, and is also liable to be seriously misinterpreted. 

 All that can be said in justification of what follows is that I am 

 under obligations to no one, either directly or by implication, 

 except as necessitated by truth and fair dealing, and that all 

 matters of personal interest are thoroughly placed aside, if I am 

 capable of so doing. The articles used are all owned by myself 

 or by the institution in whose service I am, with ©ne somewhat 

 conspicuous exception, and that was loaned to me, upon request, 

 for the purposes of this paper. No comparison is made with 

 such as I have not had abundant opportunity to test, and, with 

 the exception just mentioned, with none that have not been in 

 use during some years of time. 



In the paper upon stands, a note was made upon the fact that 

 we are prone to like best that with which we become acquainted. 

 In the case of objectives, however, there is less room for such 

 preference, because the mere handling of one is practically that 

 of others, including the position and movements of one's body 

 when at work. To be sure, in order to get the very best results 

 with a high quality objective, one must patiently learn to use 

 that particular instrument ; but this is another thing. The force 

 of habit has little to do in this last case, while it is exceedingly 

 strong in the method of moving the object under the lens, and 

 in the manipulations generally of the stand. 



It should also be stated that my work has chiefly been upon 

 uncolored objects mounted in water, with or without the addi- 

 tion of carbolic acid or glycerine, and upon colored objects in 

 balsam ; the main exception is that of Diatoms in balsam, and in 

 this case as a test for the objective rather than work upon the 

 objects for their own sake. 



MAGNIFICATION. 



Whatever may be the facts in regard to the use of high power 

 eye-pieces to secure the requisite magnification in mere tests, 

 for long continued work over the tube anything in the upper 

 end of less than about one inch focal length is unsatisfactory to 

 me. The strain upon the eye is certainly less with the medium 

 and low power oculars, and the image is better to my eye, even 

 with the finest objectives made. I choose, therefore, such focal 

 length in the objective as will give suflSicient magnification with 

 a fluygbenian eye-piece, amplifying about ten times as the upper 



