CH. IX] MICRO-PROJECTION WITH HOUSE CURRENT 285 



For example, with direct current of 10 amperes one can accom- 

 plish a great deal in micro-projection if the manipulation is skillful. 

 To get equally brilliant results with alternating current would 

 require 30 to 40 amperes of current. The heating is also excessive 

 with the high amperages. (See Ch. XIII, 768). 



If alternating current must be used for projection with the micro- 

 scope, one should not expect too much, but get as good results as 

 possible by observing carefully the conditions giving good screen 

 images, viz., apparatus in perfect order and alignment on one axis; 

 a good screen and a dark room. 



It is not wise, according to our experience, to try to use more than 

 25 amperes alternating current for micro-projection, and it is better 

 as regards the specimens and apparatus, to be satisfied with the 

 results which can be obtained with 15 to 20 amperes. An arc 

 lamp with carbons at right angles is to be preferred. 



416. Centering the apparatus on one axis, separating the 

 elements properly and the conduct of an exhibition are precisely 

 as for the direct current light. The results, however, cannot be 

 made as satisfactory, although, as stated above ( 412), by care and 

 skill much can be accomplished. 



THE PROJECTION MICROSCOPE ON THE HOUSE ELECTRIC LIGHTING 



SYSTEM 



417. As with the magic lantern ( 127), the small electric 

 current (4 to 6 amperes) available from the regular house lighting 

 system gives very gratifying results. 



Small carbons (6-8 mm. diam.) are employed and either one 

 of the small arc lamps especially designed for the purpose or an 

 ordinary arc lamp with adapters or bushings can be used. 



Of course the direct current is much more effective, but even with 

 the alternating current, which is now so common in lighting sys- 

 tems, successful projection with the microscope can be done. 



The small carbons form a minute crater, and thus approximate 

 closely to a point source of light, which is the ideally perfect source 

 from the optical standpoint. From our experience this is a 



