i8 7 i.] 



Electricity. 



561 



silvered mirror would serve for the final reflection as efficiently as a metal 

 speculum or glass silvered by Foucault's plan, which are so difficult to obtain 

 and keep in order. Faraday and Tyndall, the speaker further remarked, had 

 employed an electric lantern turned on its back to throw images on the 

 ceiling, and he himself had tried the same thing with a lime-light, and with a 

 square prism had endeavoured to direct the rays on the screen, but with results 

 unsatisfactory for reasons presently to be stated. 



Mr. C. J. Woodward had also described a similar arrangement in the 

 " Chemical News," vol. xix., p. 21. But last summer during a visit to 

 Cambridge, Professor Cooke had kindly shown him in operation a lantern, in 

 which the light was first thrown in a vertical direction by a mirror placed in 

 front of the condensers, then passed through the horizontal object and object- 

 glass, and lastly, was projected towards the screen, by a mirror silvered on its 

 face. The only drawback to this instrument was, that the object being practi- 

 cally removed to some distance from the condensers, the field of light on the 

 screen was shaded and discoloured. 



Fig. 24. 



The arrangement adopted by Professor Morton, and operating with such 

 success that with it experiments were lately shown with striking effect in the 

 Academy of Music, in Philadelphia (a building seating more than 3000 

 persons), was as follows : — 



The lantern condenser in the first place is made of three lenses, the first 

 two of such curves as to give with the light placed at about two inches from 

 the nearer one a practically parallel beam. This beam is received upon a 



