288 CONTINUOUS VIBRATORY MOVEMENT OF 



rays are characterized by differences of refrangibility or of velocity analogous to 

 those which disting-uish from one another the colors which compose white light, 

 and these differences have been proved as rigorously in regard to heat as to light. 



These specific qualities of calorific rays correspond to the lengths of different 

 vibrations which are propagated in the homogeneous ether, or in the void spaces_ 

 of ponderable matter, and which are capable of being transmitted more or less 

 easily in diathermic mediinns, according to the nature and density of the latter. 

 The calorific waves are analogous to the sonorous waves which ai"e propagated 

 in the air, and which cause the elastic bodies with which they come in contact to 

 vibrate. 



The invisibility of calorific rays in nowise diminishes the great probability of 

 the hyjjothesis which considers light and heat as modifications of the same 

 mechanical principle. In fact, visibility and invisibility depend solely on tlie 

 conforuiation of our eye, (capable of responding only to determinate molecular 

 movements,) and not on the nature of the force which produces the luminous and 

 calorific sensations. 



The limited impressibility of our retina prevents us from perceiving the chemical 

 rays situated beyond the violet extremity of the spectriun and the calorific rays 

 jilaced beyond the red extremity. The former are constituted by vibrations too 

 rapid and waves too short, the second by viV)rations too slow and waves too long. 

 But it is not certain that these two kinds of vibrations may not be visilde for 

 other living beings. What do we know of the perceptions which conduct the 

 carrier-pigeon to its distant home, or of those which affect the antennte of the 

 insect and apprise it of danger ? What of the telescopic view of the vulture, which 

 precipitates itself towards its prey before it even appears to our eyes as a visible 

 point on the horizon ? We are compelled to admit that, on the earth, in the air, 

 and in the water there are beings so organized as to perceive sounds inaudible to 

 our eais, as well as luminous ravs and colors of which we have no idea. Our 

 pei'ceptions and faculties are limited to a very small portion of the immense 

 chain of existences which stretches between the Creator and nothing. 



We believe it would be difficult to find a natural phenomenon which does not 

 give rise to a development of electricity. Both mechanical and chemical actions, 

 both light and heat, produce electricity. Thus, though it occasions numerous 

 phenomena completely different from the other mjTuifestations of the activity of 

 matter, electricity is found to be so intimately connected with those other phe- 

 nomena that we are led to admit that it depends also on the same mechanical 

 principle as heat and light. The experiments of Nairne, confirmed by those of 

 M. Eecquerel, have taught us that metallic wires traversed by an electrical dis- 

 charge, incapable of melting but sufficient to redden them, become shorter at the 

 same time that their diameter is increased. Such wires, when traversed by a 

 certain number of electric discharges, take an undulatory fonii which indicates a 

 movement of the molecules of the wire perpendicularly to its length. Van Marura, 

 towards the close of the last century, caused the discharge of his gigantic battery 

 to pass through a tin wire placed horizontally on a sheet of paper. Under this 

 action the wire was dissipated, leaving on the paper yellow traces, transversely- 

 disposed as regards the direction of the discharge ; each of these traces had a 

 peculiar texture, and all were arranged symmetrically at distances equal or 

 multiple as among themselves. Some years earlier, Beccaria had made analo- 

 gous experiments, and had interpreted the results by referring them to the prin- 

 ciple of vibrations. 



INly own investigations have also been directed to this interesting subject, and 

 I propose, on the present occasion, to repeat before my auditors the experiments 

 of this kind which 1 have instituted, and to reproduce the results which I had 

 the honor of submitting to the phj'sicists of the ninth reunion of Italian savants 

 at Venice. 



On causing the discharge to pass through a gilt thread of silk, certain parts of 



