THE MJCKOSCOPE. 23 



now holds a very high rank among philosophical implements, 

 while the transcendant beauties of form, color and organization, 

 which it reveals to us in the minute works of nature, render it 

 subservient to the most delightful and instructive pursuits. 

 To these claims on our attention, it appears likely to add a 

 third of still higher importance. The microscopic examination 

 of the blood and other human organic matter will in all proba- 

 bility afford more satisfactory and conclusive evidence regard- 

 ing the nature and seat of disease than any hitherto appealed 

 to, and will of consequence lead to similar certainty in the 

 choice and application of remedies. 



We have thought it necessary to state thus at large the claims 

 of the modern achromatic microscope upon the attention of the 

 reader, as a justification of the length at which we shall give 

 its recent history and explain its construction; and we are fur- 

 ther induced to this course by the consideration that the sub- 

 ject is entirely new ground, and that there are at this time not 

 more than two or three makers of achromatic microscopes in 

 England. 



Soon after the year 1820 a series of experiments was begun 

 in France by M. Selligues, which were followed up by Frauen- 

 hofer at Munich, by Amici at Modena, by M. Chevalier at 

 Paris, and by the late Mr. Tulley in London. In 1824 the last- 

 named excellent artist, without knowing what had been done 

 on the Continent, made the attempt to construct an achromatic 

 object-glass for a compound microscope, and produced one of 

 nine-tenths of an inch focal length, composed of three lenses, 

 and transmitting a pencil of eighteen degrees. This was the 

 first that had been made in England; and it is due to Mr. Tul- 

 ley to say, that as regards accurate correction throughout the 

 field, that glass has not been excelled by any subsequent com- 

 bination of three lenses. Such an angular pencil, and such a 

 focal length, would bear an eye-piece adapted to produce a 

 gross magnifying power of one hundred and twenty. Mr. Tul- 

 ley afterwards made a combination to be placed in front of the 

 first mentioned, which increased the angle of the transmitted 

 pencil to thirty-eight degrees, and bore a power of three hun- 

 dred. 



While these practical investigations were in progress, the 



