HEAT. 



form any distinct idea of anything capable of 

 being excited, and communicated in these ex- 

 periments except it be MOTION." 



Sir Humphrey Davy, the associate of Eum- 

 ford, in the Eoyal Institution, adopted these 

 views concerning heat. He instituted some 

 delicate experiments by which they were strik- 

 ingly confirmed. One of these consisted in 

 rubbing two pieces of ice together in a vac- 

 uum, at a temperature below the freezing 

 point. The heat of friction melted the ice. The 

 old explanation of the fact was that the friction 

 liberated the latent caloric of the ice. To this, 

 Davy replied; "If I by friction liquefy ice, I 

 produce a substance which contains a greater 

 absolute amount of heat than the ice ; and in 

 this case it cannot with any show of reason be 

 affirmed, that I merely render sensible the heat 

 hidden in the ice, for that quantity is only a 

 small fraction of the heat contained in the 

 water." Davy also propounded the hypothe- 

 sis of atomic vibrations or oscillations, as the 

 cause of thermal phenomena. This cannot be 

 better stated than in his own words: "It 

 seems possible to account for all the phenom- 

 ena of heat, if it be supposed that in solids 

 the particles are in a constant state of vibra- 

 tory motion, the particles of the hottest bodies 

 moving with the greatest velocity, and through 

 the greatest space; that in fluids and elastic 

 fluids, besides the vibratory motion, which 

 must be conceived greatest in the last, the par- 

 ticles have a motion round their own axes with 

 different velocity, the particles of elastic fluids 

 moving with the greatest quickness, and that 

 in ethereal substances the particles move round 

 their own axes, and separate from each other, 

 penetrating in right lines through space. Tem- 

 perature may be conceived to depend upon the 

 velocity of vibrations; increase of capacity in 

 the motion being performed in greater space ; 

 and the diminution of temperature during the 

 conversion of solids into fluids or gases, may 

 be explained on the idea of the loss of vibra- 

 tory motion, in consequence of the revolution 

 of particles round their axes, at the moment 

 when the body becomes fluid or aeriform, or 

 from the loss of rapidity of vibration in conse- 

 quence of the motion of the particles through 

 space." 



The researches of Davy upon this subject 

 may be regarded as continuing those of Count 

 Rumford. In 1812 he wrote : " The immediate 

 cause of the phenomena of heat, then, is motion, 

 and the laws of its communication are precisely 

 the same as the laws of the communication of 

 motion." Seguin in 1819 published a work 

 entitled De V Influence des Chemins de Fer, in 

 which he shows that the old theory lead to 

 the absurd conclusion, that a limited quantity 

 of heat can produce an unlimited quantity of 

 chemical action. He says: "It appears to 

 me more natural to suppose that a certain 

 quantity of caloric disappears in the very 

 act of the production of the force or mechan- 

 ical power, and reciprocally the mechanical 

 VOL. in 32 A 



HILDRETH, SAMUEL P. 



497 



force which disappears during the lowering of 

 the temperature of a gas is the measure and 

 the representation of the elimination of heat." 



The time had now arrived for the reception, 

 of these views by many minds, and accordingly 

 we find that, during the next ten years, emi- 

 nent scientific men in England, France, Ger- 

 many, Denmark, and America, devoted them- 

 selves with assiduity to their theoretical and 

 experimental development. In 1850 Joule's 

 law was established, which placed the subject 

 upon an immovable experimental basis. While, 

 during the same year, Dr. Carpenter formally 

 extended the research so as to include the vital 

 forces. His paper on the correlation of the 

 physical and vital forces, was published in the 

 philosophical transactions for that year. From 

 that time, the views have been gradually ac- 

 cepted by scientific men, until they may now 

 be regarded as generally established. Science 

 has thus changed her standpoint, and all phe- 

 nomena are presented in a new light. The 

 most important results alike to science, philos- 

 ophy, and education, may be expected to fol- 

 low this revolution of scientific thought. 



HILDRETH, SAMUEL PKESCOTT, M. D., an 

 American historian and physicist, born in Me- 

 thuen, Massachusetts, Sept. 30th, 1783, died 

 at Marietta, Ohio, July 24th, 1863. His boy- 

 hood was passed on his father's farm, until he 

 was fifteen years old, his primary education 

 being received at a common school. From 

 thence he was sent to Phillips Academy, An- 

 dover, and the Franklin Academy, in the 

 North Parish. He studied medicine with Dr. 

 Thomas Kittridge, a noted surgeon of Andover, 

 and received a diploma from the Medical So- 

 ciety of Massachusetts in Feb., 1805. He com- 

 menced the practice of his profession in New 

 Hampshire, but, in 1806, having made up his 

 mind to settle in Ohio, journeyed thither on 

 horseback, and after spending about two 

 months in Marietta, located himself at Belpre, 

 where, in 1807, he married Miss Cook (former- 

 ly of New Bedford, Mass.). He was very suc- 

 cessful in practice ; but, in 1808, removed to 

 Marietta, where the duties of his profession 

 were less arduous, and where he remained to 

 the close of his life. In 1810 and 1811 he 

 served in the Ohio Legislature as a supporter 

 of the administrations of Jefferson and Madi- 

 son ; but on the formation of the republican 

 party, in 1854, he connected himself with it. 

 For a period of nearly forty years he was a 

 contributor to " Silliman's Journal of Science," 

 his articles embracing a wide range of scien- 

 tific subjects, but more especially devoted to 

 meteorology, geology, and palaeontology. In 

 1837 he was a member of the Geological Sur- 

 vey, and delivered the annual address at Cleve- 

 land, before the Medical Society, of which he 

 was then president, giving a history of the dis- 

 eases and climate of Southeastern Ohio, from 

 its settlement, which was published by the So- 

 ciety. The same year he published a history 

 of the settlement of Belleville, Western Vir- 





