THE MICEOSCOPE. 35 



fluid was, as it were, formed into a concave lens, and if the 

 radius of the outward surface were such as to correct the dis- 

 persion, we should have a perfect achromatic microscope, both 

 simple and compound. This method, however ingenious, was 

 attended with considerable inconvenience, and our eminent 

 and time-honoured philosopher was led to the construction of 

 a permanent achromatic object-glass, by placing some butter 

 of antimony between a meniscus and a planoconvex lens of 

 crown-glass ; the antimony was retained between the glasses 

 by capillary attraction, and could be removed as often as its 

 properties were deranged. 



About this period, 1812, we find that numerous experi- 

 ments were carried on by Professor Amici, of Modena, to 

 improve the achromatic object-glass, and during his investiga- 

 tions he invented a reflecting microscope, far superior to 

 those of Newton, Baker, or Smith, which had been made as 

 early as the year 1738, and had been abandoned for many 

 years; this invention so far excelled any microscope pre- 

 viously made, that Amici was induced, in 1815, to lay aside 

 his experiments on the refracting instrument for a con- 

 siderable period. An account of this microscope having soon 

 reached England, Dr. Goring, in 1824, with the assistance of 

 Mr. Cuthbert, succeeded in greatly improving it, and for a 

 few years it was the most perfect form of microscope 

 manufactured in this country; but, owing to the difficulty 

 in constructing the reflectors, and the great trouble in ma- 

 naging them, this instrument, like the reflecting telescope, 

 fell into disuse, and even Amici himself entirely abandoned 

 it, and returned to his former experiments on the refracting 

 achromatic object-glasses. 



In the year 1816, Frauenhofer, a celebrated optician of 

 Munich, constructed object-glasses for the microscope of a 

 single achromatic lens, in which the two glasses, although in 

 juxta position, were not cemented together, these glasses were 

 very thick and of long focus ; but although such considerable 

 improvements had been made in the telescopic achromatic 

 object^lass since its first discovery by Euler in 1776, we find 

 that even at so late a period as 1821, M. Biot wrote, "that 

 3* 



