120 TRANSACTIONS OP THE 



convex surfaces. The tube in which the lenses were inclosed was 

 as large as a man's leg, and the eye-glass as broad as the palm of 

 the hand. It had four draws magnifying from 41 to 143 

 diameters, and must have been an instrument looking more like 

 a cannon than one of our present microscopes. Philip Bonnani's 

 was similar, but was placed horizontally and had beneath its stage 

 a convex lens which condensed the light on tbe object. This was 

 the first microscope with a condenser, and the account of it was 

 published in 1698. 



In 1738 Lieberkuhn gave his solar microscope to the world, 

 which, owing to its enormous magnifying power and to the ease 

 with which it exhibited the minute wonders of nature to a large 

 audience, drew universal attention to the microscope. In 1742 

 Henry Baker, F.B.S., published an admirable treatise on the 

 microscope, which was soon followed by others. In 1811 

 Frauenhofer, a celebrated optician of Munich, constructed the 

 first achromatic object-glasses for the microscope, in which the two 

 glasses, although in juxtaposition, were not cemented together. 

 Although considerable improvements in the making of achromatic 

 object-glasses had taken place since their first discovery by Euler 

 a German mathematician, in 1776, opticians at that time enter- 

 tained the opinion that it would be impossible to make a good 

 achromatic microscope. Dr. Wollaston, the inventor of the 

 celebrated doublet named after him, also thought that the com- 

 pound microscope would never rival the single. Further experi- 

 ments conducted by Selligues, Frauenhofer, Professor Amici of 

 Modena, Chevalier in Paris, and Dr. Goring in London, resulted 

 in Selligues making the first compound object-glass composed of 

 four achromatic compound lenses each consisting of two lenses 

 which could be used combinedly or separately. In 1824 Mr. 

 Tulley, at the suggestion of Dr. Goring, constructed an achromatic 

 object-glass for a compound microscope of 9-lOths of an inch focal 

 length, composed of three lenses transmitting a pencil of 18 

 degrees, the first achromatic object-glass ever made in England. 

 In 1825 Chevalier made an achromatic objective of four lines 

 focus, and in 1827 Amici brought to England a horizontal 

 microscope the object-glass of which consisted of three superposed, 

 achromatic lenses of large aperture. In 1829 Mx. Jackson Lister 

 proposed a combination of lenses upon the theories of achromatism 

 propounded by Sir John Herschel, Professors Sir George Airy, 



