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 

 * l 180." Why should there be " a law to prevent it ?" 



Now, professor, if this 180 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 " 180." Will you be kind enough to 

 name the extreme angle immediately adjacent, but not contact- 

 ing the impossible and the absurd ? 



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

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

 have it, and the "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 from 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 ]80, plus 180, 

 or 180 X 45 a , 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- 



