CONSTRUCTION OF THE MICROSCOPE. 



55 



To see these lines at all, it is requisite to use a micro- 

 scope with a magnifying power of 100 diameters; the 

 bands containing the fewest number of lines will then be 

 visible. To distinguish the finer lines, it will be necessary 

 to use a magnifying power of 300, and then the lines which 

 are only l-4700th of an inch (Prussian) apart will be 

 seen perfectly traced. Of all the tests yet found for 

 object-glasses of high power, these would seem the most 

 valuable. These tracings have tended to confirm the 

 undulating theory of light, the different colours of the 

 spectrum being exhibited in the ruled spaces according to 

 the separation of the lines ; and in those cases where the 

 distances between the lines are smaller than the length of 

 the violet-coloured waves, no colour is perceived ; and it 

 is stated, that if inequalities amounting to -000002 line 

 occur in some of the systems, stripes of another colour 

 would appear in them. 



Achromatic object-glasses for microscopes are of various 

 foci, differing from 2 inches to l-50th of an inch. 



Magnifying Power of Mr. Ross's Object-Glasses with his 



various Eye-Pieces. 



