APPLICATIONS OF THE ELECTRIC LIGHT. 285 



\hQpolyorama, adapted to the lantern for certain experiments. 

 Finally, in the side of the lantern is a small bull's-eye, with a 

 violet glass, by which the condition of the light is examined. 

 In order easily to regulate the position of the luminous point,, 

 which in some experiments must be fixed in the most exact 

 manner, the regulator is placed on a stand which can, by 

 means of two screws, be moved in two rectangular directions 

 (up-and-down and sideways). ' 



The projections may be made at any distance ; only they 

 lose their brightness and clearness where the distance is out 

 of proportion to the intensity of the light : 5 metres is com- 

 monly the most suitable distance for the light from a battery 

 of fifty elements. We show in Fig. 7 2 an experiment of this 

 kind. 



The magic lantern gives, with the electric light and Levy's- 

 or Favre and Lachenal's transparent photographic views, 

 effects so striking that a spectator would fancy he is tran- 

 sported to the very spot ; and such a perfection in the views 

 is now attained that the objects sometimes seem to stand out 

 in relief, as in the effects of the stereoscope. This method of 

 projection is now much used commercially, and, besides 

 Duboscq's apparatus, which are applicable to every kind of 

 optical experiment, there are those of Molte'ni, which are ex- 

 clusively adapted for this kind of application. 



Among the projection experiments that have been made 

 by these apparatus, we may particularly mention that of the 

 reading of microscopic despatches forwarded during the siege 

 of Paris by carrier-pigeons ; these despatches, each of which 

 covered less than a square millimetre, were easily read before 

 the multitude of those who were interested in receiving news 

 from the provinces. Fig. 73 represents this application of 

 the electric light. 



The electric light has also been used for the photographing 

 of places or objects not otherwise illuminated. In this way 

 Levy has reproduced the pretty fountain under the staircase 

 of the Grand Opera, and certain English and American 



