1865.] REVIEW— TOUMANS ON FORCE. 159 



science has opened to us, before we find ourselves enveloped in 

 those thick mists, which on every side bound the horizon of the 

 human intellect!' 



" Rumford's experiments completely annihilated the material 

 hypothesis of heat, while the modern doctrine was stated in explicit 

 terms. He moreover advanced the question to its quantitative 

 and highest stage, proposing to find the numerical relation between 

 mechanical power and heat, and obtained a result remarkably near 

 to that finally established. The English unit of force is the foot- 

 pound, that is, one pound falling through one foot of space ; the 

 unit of heat is one pound of water heated 1°F. Just fifty years 

 subsequently to the experiment of Rumford, Dr. J. P. Joule, of 

 Manchester, England, after a most delicate and elaborate series of 

 experiments, determined that 772 units of force produce one unit 

 of heat ; that is, 772 pounds falling through one foot produces 

 sufficient heat to raise one pound of water 1°F. This law is 

 known as the mechanical equivalent of heat. Now, when we 

 throw Rumford's results into these terms, we find that about 940 

 units of force produced a unit of heat, and that, therefore, on 

 a large scale, and at the very first trial, he came within twenty per 

 cent, of the true statement. No account was taken of the heat 

 lost by radiation, which, considering the high temperature pro- 

 duced, and the duration of the experiment, must have been con- 

 siderable j so that, as Rumford himself noticed, this value must be 

 too high. The earliest numerical results in science are rarely 

 more than rough approximations, yet they may guide to the 

 establishment of great principles. Certainly no one could question 

 Dalton's claim to the discovery of the law of definite proportions, 

 because of the inaccuracy of the numbers upon which he first 



rested it. 



^ ^ * ^ %. ^ * 



" Those doctrines [of the correlation and conservation of forces] 

 have received their subsequent development in the various direc- 

 tions, by many minds, but we may be allowed to question if the 

 contributions of any of their promoters will surpass, if indeed 

 they will equal, the value and importance which we must assign 

 to the first great experimental step in the new direction. 



" The claims of Rumford may be summarized as follows : 



I. He was the man who first took the question of the nature 

 of heat out of the domain of metaphysics, where it had 



