396 HOW TO SEE WITH THE MICROSCOPE. 



Why do you accuse Messrs. Tolles and Spencer of perpetrat- 

 ing acts that are absurd and impossible ; and why do you ven- 

 ture to hint that one of these gentlemen attempts to " lead 

 scientists by the nose," (whatever that may mean). The names 

 of Spencer and Tolles are revered by American microscopists, 

 and their unrivaled efforts in the improvement of object-glasses 

 have won for them a world-wide reputation. The chances are 

 that they know more of microscope optics than you and I put 

 together; and these are the men who mark their objectives 

 4t 180." Why should there be kt a law to prevent it V" 



Now, professor, if this 18*0 is impossible and absurd, will you 

 kindly inform the readers of this journal what figures Tolles 

 and Spencer ought to engrave on their wide-angled objectives 

 in place of the awful tfc 180." Will you be kind enough to 

 name the extreme angle immediately adjacent, but not contact- 

 inQ the impossible and the absurd ? 



Again I read, " plus 180 does riot mean 97 balsam." Did I 

 assert this V Now, I ask what does 97 balsam mean ? Let's 

 have it, and the a why" thereof. Unless you can tell me exactly 

 what the 97 balsam angle is, I shall not take any stock in your 

 above assertion. 



Once more, you say that "true apertures can be measured 

 and definitely stated." I wish that you would tell Mr. Wenham 

 how the thing is done ; he tried for a whole year to measure one 

 of Tolle's objectives, without getting any two results alike ! 

 But I am after you, not Wenham. I desire to learn irom you 

 precisely what " true aperture is." When thus taught, then 1 

 desire to know by what physical process the same can be meas- 

 ured " definitely" you know. "Accuracy" is the thing we 

 scientists want. 



Now, my dear sir, I call on you to answer all of these inter- 

 rogatories, and when you shall have proven that 180, plus 180, 

 or 180 X 45, are one and the same thing ; when you shall 

 show that Messrs. Tolles and Spencer are asserting absurd and 

 impossible things, and more, are trying to lead scientists " by 

 the nose ;" when you shall prove that a thorough physicist 

 can know nothing of balsam or fluid mounts ; when you shall 

 have demonstrated that I should have apologized to my Dun- 



