SUPPLEMENT. 375 



DISCURSORY THOUGHTS RELATING TO THE USE AND ABUSE 

 OF THE MICROSCOPE. 



An Address delivered by Prof. J. Edwards Smith, before the Dunkirk 

 Microscopical Society, Tuesday Evening, October 31, 1876. 



To the Members of the Dunkirk Microscopical Society : 



GENTLEMEN: About twelve months ago a friend of mine and 

 a brother microscopist, ordered from London a low-angled l-4th 

 inch objective ; my friend was engaged in histological investiga- 

 tions, and felt the need of a reliable medium-power glass. He 

 had been told that wide-angled glasses, although very suitable 

 for the purposes of the diatomist, were hardly suitable for the 

 work he had in hand; he was told, too, that the thing needed 

 was a glass of low or moderate angle, say from 50 to 70, and 

 one that had great working distance ; in short, as the saying 

 goes, he needed a good " working glass." 



In due time the objective was received, and one very pleasant 

 evening my friend called on me expressly to show the work of 

 the lens. I remember that we had a very enjoyable time, amus- 

 ing ourselves by looking over a variety of specimens suitable 

 for the glass. In the course of the evening he exhibited a beau- 

 tiful section of a human tooth, and placing the same under the 

 l-4th, called my attention to the "Nasmyth's membrane," 

 described by Frey and others. 



This was a matter of interest to me, for I had heard much of 

 this " Nasmyth's membrane ;" I had examined human teeth 

 time and time again with my own wide-angled glasses, but had 

 never been able to discover the same. I was, in fact, somewhat 

 curious about the matter. It seemed odd, to say the least, that 

 my glasses, which would show me clearly and accurately, lines 

 as close as 120,000 to the English inch, should fail to show me 

 the existence of a membrane said to be about 1-6,000 of an inch 

 in thickness ; and then again I had hunted with a low-angled 

 l-4th of my own without success. Hence it was with expect- 

 ancy and interest that I put my eye to the tube ; I saw a 

 decided thickening of the margin of the crown of the tooth, and 

 was informed that this was the veritable " Nasmyth." But, 



