456 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



which, with proper gearing, was moved by two horses. The cylinder was 

 placed in a vertical position and filled with water. By the friction of the 

 plunger and cylinder the water was gradually heated, and at the end of 

 two hours and a half it actually boiled. Of course it was quite apparent 

 that the process could be continued for any length of time and heat be 

 constantly generated. Although this experiment proved decisively that 

 heat was the result of motion, still the majority of scientific men continued 

 to regard heat as matter; and that portion which entered bodies without 

 increasing their temperature, they called latent heat. The Scotch philoso- 

 pher, Dr. Black, in 1780, was the most prominent of the advocates of the 

 material theory, and his explanations of all phenomena regarding heat have 

 been accepted and promulgated in nearly all seminaries of learning down 

 to the present day. Many teachers there were, undoubtedly, who inclined 

 to the motion theory, yet continued to present his views because they could 

 be quite readily comprehended by the pupil. 



After the explanation of the manner in which a ray of light is polarized 

 by the peculiar action of transverse vibrations, Melloni turned his attention 

 to the action of heat in the sunbeam, and demonstrated that its rays, too, 

 could be polarized, and the natural inference followed that heat is the 

 result of undulations moving around, and in all directions transversely to 

 the line of the ray. How this motion is modified after the entrance of the 

 heat ray into a ponderable body is still a mystery. That its effect is to 

 push asunder the molecules or atoms and counteract the force of cohesion, 

 and at the same time give an axial motion to such atoms when the body 

 has assumed a liquid or gaseous form, must be admitted. The internal 

 action of the heat force in ponderable matter presents a vast field yet to be 

 explored. 



Heat as well as light being considered to be the result of wave motions 

 of extremely subtle ethereal fluids, it becomes an interesting query whether 

 these effects, as well as that of actinism, are not due to the diverse action 

 of the same fluid. This hypothesis enables us to form a conception of the 

 manner in which these several forces act, while it is quite imposf-'ible to 

 conceive how a separate and distinct fluid, for each of these forces, as 

 well as those of electricity and magnetism, can act simultaneously. The 

 plausibility of the hypothesis is increased by an examination of the 

 decomposed sunbeam. 



If a ray of light enters and is passed through a glass prism, its spec- 

 trum presents to the eye seven colors in the following order: red, orange, 

 yellow, green, blue, indigo and violet, the last having the greatest refrang- 

 ibility and the first the least. The number of undulations of the ethereal 

 medium producing each color, increases from the red up to the violet. By 

 the use of the electro-pile of Nobili, it hag been discovered that the amount 

 of heat in the violet ray is least, and that it increases in each color to the 

 red; but what is most remarkable, the heat increases far beyond the red 

 ray among the invisible rays of least refrangibility. On the other hand, 

 the chemical effect known as actinism, upon which the photographer relies 

 for his picture, increases from the blue to the violet. 



In papers read before the American Photographical Society, he, the 

 Chairman, had endeavored to show that these three solar effects, heat, 



