SUPPLEMENT. 367 



over the tube " would convince Prof. Hitchcock that u the very 

 best performance (penetration, depth of focus, reach, or what 

 not included) is seen by central light. I again invite investi- 

 gation. The passage from Frey was original with Dr. Carpen- 

 ter ten years ago. I have no objection to urge. 



A word, and let it bo with due respect to Dr. Carpenter. His 

 advanced age and failing eyesight, together with his many 

 duties and cares, forbid that he should continue to be the 

 authority he has been in the past. Singularly enough, the 

 doctrines advanced by Dr. Carpenter twelve years ago are still 

 endorsed by many to-day. This operates as a brake to the 

 wheel of progress ; surely Dr. C. is not to blame. Mr. Hitch- 

 cock asks if Dr. C. has changed his opinion since the fifth edi- 

 tion of his work ; in reply, I can say that the latest information 

 I have bearing on this point is this; about eighteen months 

 since a friend of mine was in London attending medical lect- 

 ures. He sought Dr. Carpenter's advice as to objectives ; Dr. 

 C. advised him to go home and purchase the duplex, and my 

 friend did so purchase. Be all this as it may, while I enter- 

 tain the highest respect and admiration for his medical and 

 scientific attainments his life of unceasing toil in his profes- 

 sionI cannot, and for the reasons presented, attach impor- 

 tance to Dr. Carpenter's endorsement of the duplex glasses. 

 In other words, I should prefer the testimony of American 

 experts. 



To resume, Mr. Hitchcock further says that " two hours over 

 the tube " has demonstrated something, he don't say exactly 

 what. At anyrate he volunteers his thanks, which I joyfully 

 accept. I should have said that " two hours jointly over the 

 tube " would demonstrate more than volumes of print. 1 hope 

 yet to enjoy such a tete-a-tete with friend Hitchcock, and prom- 

 ise in advance to delight him with the new wide-angled l-10th 

 before referred to. The new glass, too, confirms in a truly 

 practical manner the positions I have heretofore taken in print. 



In conclusion, I have again to thank Prof. Hitchcock for his 

 good natured review of my previous article, and hope that he 

 will find nothing in this hastily written article objectionable. 



