
XV.—On the Dynamical Theory of Heat, with numerical results deduced from Mr 
JouLE’s equivalent of a Thermal Unit, and M. Reanauut’s Observations on 
Steam. By Witt1am Tomson, M.A., Fellow of St Peter’s College, Cam- 
bridge, and Professor of Natural Philosophy in the University of Glasgow. 
(Read 17th March 1851.) 
INTRODUCTORY NOTICE. 
1. Sir Humpurey Davy, by his experiment of melting two pieces of ice by 
rubbing them together, established the following proposition :—‘‘ The phenomena 
of repulsion are not dependent on a peculiar elastic fluid for their existence, or — 
caloric does not exist.” And he concludes that heat consists of a motion excited 
among the particles of bodies. ‘“ To distinguish this motion from others, and to 
signify the cause of our sensation of heat,” and of the expansion or expansive 
pressure produced in matter by heat, “the name repulsive motion has been 
adopted.” * 
2. The Dynamical Theory of Heat, thus established by Sir Humpurey Davy, 
is extended to radiant heat by the discovery of phenomena, especially those of 
the polarization of radiant heat, which render it excessively probable that heat 
propagated through vacant space, or through diathermane substances, consists of 
waves of transverse vibrations in an all-pervading medium. 
3. The recent discoveries made by Mayer and Jouxz,} of the generation of 
heat through the friction of fluids in motion, and by the magneto-electric excita- 
tion of galvanic currents, would, either of them be sufficient to demonstrate the 
immateriality of heat; and would so afford, if required, a perfect confirmation of 
Sir Humpurey Davy’s views. 
: * From Davy’s first work, entitled “ An Essay on Heat, Light, and the Combinations of 
Light,” published in 1799, in “ Contributions to Physical and Medical Knowledge, principally from 
the West of England, collected by Tuomas Beppozs, M.D.,”-and republished in Dr Davy’s edition of 
his brother’s collected works, vol. ii. Lond. 1836. ; 
+ In May 1842, Mayer announced in the “ Annalen” of Wouter and Liesic, that he had 
raised the temperature of water from 12° to 13° cent. by agitating it. In August 1843, Joure 
announced to the British Association, “‘ That heat is evolved by the passage of water through 
narrow tubes;” and that he had “ obtained one degree of heat per lb. of water from a mechanical 
force capable of raising 770 Ibs. to the height of one foot;” and that heat is generated when 
work is spent in turning a magneto-electric machine, or an electro-magnetic engine. (See his 
paper ‘‘ On the Calorific Effects of Magneto-Hlectricity, and on the Mechanical Value of Heat.” 
Phil. Mag. vol. xxiii. 1843.) 
VOL. XX. PARTI. 4B 
