204 ANNUAL OF SCIENTIFIC DISCOVERT. 



remarkable analogies with the progress of the Copernican system. The 

 theory of heat has now arrived at the same staire as had the theory of liirht 



* 



when Young made his appearance in the scientific world. Bacon's striking 

 axiom, " What is heat for sensation is motion taken under r.n objective point 

 of view; }J with the results of Rumford and Daw, caused doubts as to the 

 existence of a calorific matter ; the precise exposition of a possible transmu- 

 tation of moving into molecular force completely overthrew the oM theory. 

 Radiating heat, objectively identical to luminous rays, is the thermic phe- 

 nomenon in its abstract form ; luminous ether must therefore be considered 

 the material substratum of these phenomena. The explanation of the phe- 

 nomena of transmitted or conducted heat is connected with some more dif- 

 ficulties, but may be made more easy by the following considerations. A 

 ray falling on a material medium is partly reflected ; at the same time three 

 different effects may take place viz., a. the ray passes through the me- 

 dium, without producing any change in it ; b. the ether contained in the 

 medium is set in motion, the body is heated, or, as it is (although improp- 

 erly) said, "it absorbs heat;" (it is the absorbed heat which elevates the 

 temperature of the body, and we use this expression, because a body en- 

 dowed with sensitive faculty perceives the sensation of heat a sensation 

 determined generally, not by the quantity of motion, which constitutes the 

 quantity of heat, but by the celerity of the particles passing through the 

 position of rest;) c. the passage of the ray is attended by the excitation of 

 heat. Caloric capacity is the faculty to receive a certain quantity of liv- 

 ing power. Heat expands bodies, and this expansion is assumed as the 

 measure of temperature. This effect, however, is not the immediate result 

 of the oscillatory movement ; a portion of it, proportional to the living 

 power of the oscillation, is changed into operative power, which is the im- 

 mediate consequence of expansion. This process may be still better under- 

 stood by the action of an electric current running along a conducting wire, 

 and converting itself into heat by contriving to overcome an obstacle. A 

 similar process takes place with regard to caloric capacity whenever the 

 volume of any body undergoes any change. A body has more capacity for 

 heat (to use the still prevailing expression) whilst its volume is variable, 

 than under a constant pressure, because a portion of the heat which it as- 

 sumes is converted into operative power. 



OX THE SPHEROIDAL STATE OF LIQUIDS. 



"With respect to the cause of the singular phenomena, known as the sphe- 

 roidal state of liquids, differences of opinion still exist among men of science. 

 The appearance of the drop on the heated surface suggests the idea that the 

 liquid and metal are not in contact with each other ; such a breach of con- 

 tact, however, has been denied, and to determine this point, Poggendorff 

 devised the following ingenious experiment : 



Let a b be a section of the basin, d that of the drop ; into d let a platinum 

 wire descend, which is united with the negative pole, p, of a small galvanic 

 battery ; a second platinum wire, m n, communicates with the positive pole 

 of the battery, and is placed in contact with the metallic basin, a b. Into the 



