Account Amici's llejlecting Microscope, 187 
Professor Amici has accordingly compared the best English mi- 
croscopes of Adams and Dollond with his own, and, upon a 
comparative examination of the same objects, he maintains that 
his instrument shews the object more clearly and distinctly, 
even when magnified in the same degree. The Professor had 
no opportunity of making ^experiments with the microscope of 
De la Barre, and those made at Benedictbeuern by Utzschneider 
and Fraunhofer ; but he thinks himself justified in concluding, 
that his own admits of a far greater degree of magnifying power 
than the latter, as he perceives that their largest microscope does 
not magnify the objects above 22,500 times in the area, while his 
goes the length of a million. He has also endeavoured to shew, 
by a mathematical calculation, that such a high degree of mag- 
nifying power cannot be attained in a dioptrical instrument. 
The following, according to Amici, are the advantages of his 
microscope. 
1. The observer has the convenience of being able to examine 
the object in a horizontal position, while, in those constructed 
on the dioptrical principle, the object is examined in a vertical 
position, that is, from above. The observer, therefore, may be 
seated, has no occasion to bend his head, and can examine ob- 
jects more conveniently, or for a longer time, than with a large 
dioptrical instrument on the common construction. 
2. The different degrees of magnifying power can be easily 
and speedily applied and changed, nothing more being neces- 
sary for this purpose than to change the eye-glass, without vary- 
ing the position or distance of the object, so that it may be exa- 
mined with great rapidity in all different degrees of magnitude, 
without the least variation of the point of view ; while in the 
dioptrical instruments, it is necessary not only to change the 
object-glass, but also the visual distance, which not only occa- 
sions loss of time, but very seldom admits of the object being 
again seen in the same position, and in the same point of view. 
3. As in this new instrument the object always remains in 
the same position, and is kept constantly at the distance of half 
an inch from the body of the microscope, it consequently admits of 
our examining objects immersed in fluids, and animals swimming, 
and that nearly at an equal depth, and in every degree of mag- 
nitude. With dioptrical instruments, on the other hand, this is 
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