PRACTICAL PHOTOMICROGRAPHY. 43 



The electric light has been used with great success in this 

 connection, an arc lamp having been the usual form. There 

 is no doubt that an arc light, provided it is steady, may be 

 expected to work grandly for our purpose. It is in most cases, 

 however, expensive, difficult to work to perfection, and when 

 imperfectly worked, a very serious botheration. As the writer 

 has no experience of the arc light he refrains from making 

 any statements as to its suitability or unsuitability for our pur- 

 pose. Incandescent filaments in electric lamps might be made 

 answerable to our purpose, but so far as we know no incan- 

 descent electric lamp has yet been found equal even to a good 

 oil lamp, the area of incandescence being too slender in the 

 former. 



FlG. 11. OXY-HYDROGEN JET BY NEWTON. AUTHOR'S " CUT-OFF." 



The writer uses the lime light as his radiant in nearly all his 

 work, and, taken as a whole, this light is as nearly perfect for 

 the purpose as any illuminant at present known. The general 

 form of a lime-jet is well known, and the ordinary form of 

 "blow-through" or "mixing" jet will doubtless suffice for all 

 purposes. The blow-through jet gives a larger area of incan- 

 descent lime, but the incandescence is not so perfect, nor the 

 color nearly so good as that produced by the mixed gases. 

 There is no necessity for any great pressure of the gases, pro- 

 vided the proportion of one gas to the other is suitable, and 

 the nipple of the jet has a bore suitable to the other circum- 

 stances. All these matters maj> be settled by experiment, and, 

 in fact, must be so settled. The writer uses a mixing jet, but 

 takes the hydrogen direct from the house main, while he puts 

 the oxygen in a bag and puts thereon only a moderate pressure ; 



