23^ M. Miarianini on an analogy 



Art. VIII. — Memoir on an Analogy which exists between the 

 propagation of Light and that of Electricity, or on the con- 

 stancy of the effects of electric currents forced to traverse 

 spaces already traversed by other electric currents. By Dr 

 Et. Maria:nini, Professor of Natural Philosophy at Venice. 



Among the admirable properties with which light is endowed, 

 one of the first is certainly the extraordinary rapidity with 

 which it is propagated ; a property which, combining with the 

 subtilty of its particles, produces very probably that other 

 faculty, not less astonishing, in virtue of which the rays cross 

 each other in their route without undergoing the slightest al- 

 teration. 



We know, that on placing the eye at a small hole, before 

 which is extended a vast space on which is disseminated a 

 number and variety of objects, how distinctly they are seen. 

 This experiment clearly shows in what manner a prodigious 

 number of luminous rays may meet in a very small space 

 without experiencing a sensible collision. A phenomenon of 

 the same kind, and even still more surprising, may be pro- 

 duced by means of concave mirrors. Place two together in 

 such a manner that their optical axes intersect each other 

 reciprocally, and put before one of them any object, a red 

 ball for instance, in such a situation that the mirror reflects 

 the image to the place where its axis meets with the axis of 

 the other mirror. Place before the second mirror a different 

 object, a green ball for instance, in such a manner that its 

 image exactly strikes the place where the axes cross each other. 

 If the observer then directs his attention towards the first 

 mirror, and looks along the axis of it, he will perceive the 

 image of the red ball ; directing his eye then towards the axis 

 of the second mirror, he will see the image of the green ball 

 precisely in the same place where he had before seen the red 

 ball. This experiment plainly shows the manner in which 

 the luminous rays, proceeding from two different objects, can 

 cross each other reciprocally without experiencing the slightest 

 alteration. 



Since then electricity is not inferior to light in the facility 



