AND MODERN MICROSCOPES. 95 
Corresponding No, 
Paris tne penae Minne goats aad 
hi 1-1000 ‘ -1001 11,240 lst 
2, 1-1500 .000633 
8. 1-2000 .00053 22,480 
4. 1-2500 .0004 
5. 1-3000 .000333 
6. 1-3500 
Tano: F4000 .00025 44,960 
8. 1-4500 
9. 1-5000 .0002 56,200 15th 
lO. 1-5500 
ll. -1-6000 .000167 67,622 20th 
12... 6500 
3. -7000 000143 783737 25th 
4. 1+7500 84,4 
15. 8000 .000125 90,074 30th 
16. {8500 .000117 96,234 
17. .000111 101.484 
18. -1-0300 000105 107,167 
19. 1=10000 .000100 112,668 

Has human art ever made an instrument capable of ren- 
dering lines, 112,000 to an inch, visible? If not, is it possi- 
ble to do so? Is there anything in the laws of light, which 
renders it impossible to see lines so close, and therefore 
render useless the labors of the optician to improve his in- 
struments beyond a certain point? and, as a corollary, is it 
decided that it will be useless for the naturalist to try to 
investigate the structure of tissues beyond what the best 
existing instruments have shown? It must be borne in mind 
that the power of seeing a single object is not the question, 
but the power of distinguishing two or more objects nearly 
in contact. The problem is exactly the parallel of that of 
the power of the telescope of separating double stars. A 
brief sketch of what has been done, and what opinions on the 
problem have been expressed by eminent microscopists and 
opticians is essential to a full understanding of the question. 
Professor Quecket, in 1855, asserted that “no achromatic 
has yet been made capable of separating lines closer together 
than the -s§5s of an inch.” ‘Mr. Ross found it impossible 
to ascertain the position of a line nearer than sovo of an 
inch.” “Mr. De la Rue was unable to resolve any lines on 
Nobert’s test plate closer than gy$0s of an inch.” 
