120 THE PRESIDENT'S ADDRESS. 



diameters. In 1710 Mr. Adams gave to the Royal Society a paper 

 detailing his method of making these microscopes, and he states 

 that placing these globules of glass between silver plates, having 

 holes in them to hold the lenses, he found them act admirably. It 

 soon occurred to others that if spherical drops of glass would mag- 

 nify, spherical drops of water would do so also ; and a Mr. Stephen 

 Gray published a paper, in which he gave the necessary directions 

 for the formation of microscopes from drops of water held in sus- 

 pension from pin holes in plates of metal; but it was found that the 

 refractive power of water was not so great as that of glass, and 

 consequently these water lenses were abandoned, but subsequent 

 investigators, amongst whom we may name Sir David Brewster, 

 still tried fluid lenses, substituting viscid fluids of different degrees 

 of density for the plain water formerly used, and generally with 

 good results, but they were not found so convenient in their mani- 

 pulation as more solid material, and they were finally abandoned. 

 Opticians then, a few years after, ran to the opposite extreme, from 

 fluids to the hardest known materials ; and we find it recorded that 

 Messrs. Goring and Pritchard made lenses of diamonds, sapphires 

 and garnets, but the expense of working these, and certain faults 

 found in the diamond lenses after they were fashioned into shape 

 led to the discontinuance of their use. The smallest globules of 

 glass, and therefore the greatest magnifying powers in existence in 

 1765, were made by Signor Torre, of Naples, who sent four of 

 them to the Royal Society ; the largest of them being only g^th 

 of an inch in diameter, but said to magnify the diameter of an 

 object 640 times. The smallest was y-j-^th of an inch. What- 

 ever use Torre made of these is not stated, but Baker, who had 

 successfully worked with Leeuwenhoek's glasses, could make 

 nothing of them. Up to this period history affords us very little 

 insight into the mechanical arrangements of microscopes, for with 

 the exception of the plates used to hold these glass spheres, with a 

 point upon which to place the object in their focus, we hear of 

 nothing besides until we come to 1743, when the microscope most 

 generally known and used was Wilson's pocket microscope, and as 

 its appearance, after the simple lens and its sustaining plate, must 

 have excited some wonder and admiration I may briefly describe 

 its character. Its body was of brass, ivory, or silver. The single 

 lens doing duty as eye-piece was fastened in the end of a tube, 

 which, having a finely threaded male screw cut on its outside and 



