1 82 



OPTICAL PROJECTION 



dependent approval, especially in first-class public institutions ; 

 and, so far as I can learn anything at all about them which 

 it has b.een most difficult to do their success has been in 

 precise proportion to the degree in which the same general 

 arrangements have been adopted, though I have not as yet 

 heard of equal results having been obtained. I therefore con- 

 fine myself to what I know and have myself openly tested in 

 various public demonstrations. Moreover, everything in this 

 chapter except the description and explanation of the instru- 

 ment in detail, will apply equally to others in proportion to 

 the efficiency of their performance. 



92. The Oxy-hydrogen Microscope. Fig. 102 gives a sec- 

 tion of the instrument as constructed for the oxy-hydrogen light. 



AM 



Pio. 102. Oxylijdrogen Microscope 



o represents the lantern condenser, which I prefer to make 

 5 inches in diameter and of triple form, so as to take up an 

 angle of 95, and bring the rays to a focus, if let alone, at 

 about 6 inches in front of the front lens. If the microscope 

 be required to fit an ordinary 4-inch lantern front, the arrange- 

 ment must be slightly different, the lime being in this case 

 pushed up so as to give an approximately parallel beam with 

 the ordinary double condenser, while a third lens either slides 

 or racks in the back-end of the microscope, so as to bring 

 the parallel rays to a focus corresponding in character to the 



