The UnpiiUiskcd Papers of J. J. Lister. 31 



21. Well-holder . Does it fit on easily, and does the rod slide 



smoothly ? 



22. Forceps . . Does it fit on easily, and does the rod slide 



smoothly ? 



23. Side illuminator Does it fit on easily, and does the rod slide 



smoothly and without slipping ? 



24. Is the ball-and-socket joint safe and tight ( 



25. Pillar ... Is the joint properly firm ; is pin fixed, to 



stop it ; and is pillar tight ? 



26. Bullseye lens — Live-box — Glass trough and holder — Glass 



plates, etc. 



27. Case ... Is the packing complete ? 



28. Is list made of the powers ? 



[But apart from these and many other notes on the construction of 

 the Microscope, there are two unpubHshed manuscripts among the papers 

 which undoutedly amount to a startUng revelation, for they show J. J. 

 Ijister as a remarkably keen and clever investigator of an interesting 

 and important problem, which at his time and indeed for long after had 

 only been nibbled at by others— the resolving power of optical instru- 

 ments, including the human eye. The later of the two MSS. is now 

 published for the first time, exactly as left by the author, who apparently 

 finally revised it in 1853, ten years before his death. There would seem 

 to have been some mysterious reason which caused him again and agnin 

 to postpone publication, until in the end it remained unpublished till 

 now, just 50 years after the author's death. 



Nothing could better show the value of this work than the unques- 

 tionable fact that even now it contains much that is of great scientific 

 interest ; had it been published — as it might have been in the thirties 

 of last century — it would have anticipated much of the work done forty 

 years later by Abbe, Helmholtz, and others. 



That there was some reason why Lister did not publish his paper 

 appears certain from the following letter and enclosure addressed to him, 

 which evidently was never acted upon, the permission even to publish 

 the table of resolving powers based on this experimental work being 

 refused :] 



" 30 Church Street, Spitalfields, 



April 7, 1841?. 



"My Dear Sir, 



From the data which you kindly gave me, I deduced a short 

 logarithmic formula, by which I have calculated the accompanying 

 table. On showing it to Mr. Warren Delarue, he offered to have it 

 set up at his manufactory, and a few copies struck off on cards for 

 private distribution among a small circle of microscopists. It 

 struck me that you might object to having any portion of the 

 results of your researches printed before you had submitted the 



