356 
BIGELOW. 
much about the operations of nature roughly classified as 
heat. The story of this attempt to solve the main problem 
is worth repeating (Compare Energetik, Helm). The dis¬ 
covery that combustion must be ascribed to a process and 
not to a substance, and the later proof that heat is a process 
and not a substance, brought up the entire range of questions 
involved in natural process, and with them the study of 
the primary problems: What is force? What is energy? 
A long controversy arose over the proper measure of force. 
Some said, It is the motion generated, and hence where there 
is no motion there is no force. Others claimed that the ac¬ 
celeration of motion, the rate at which velocity of motion 
changes, is the true measure of force, and these still hold the 
field. Helmholtz defined energy as E — v 2 in 1847. It 
had already been surmised that heat is a form of motion. 
Hobbes thought that light and heat had a common origin in 
motion; Locke that heat is only motion ; J. Bernouilli had 
the conception of the conservation of energy; Daniel Ber¬ 
nouilli suggested the kinetic theory of gases ; Count Rumford 
boiled water by means of friction only; Humphrey Davy 
melted ice by rubbing two pieces over each other; Fresnel 
showed that light and heat are interchangeable; Mohr dis¬ 
cussed the transformation of forces; Lagrange found the 
dynamic equation of a conservative system of forces. The 
practical mechanicians soon saw that the transformation of 
forces leads to the idea of the conservation of energy. Poncelet 
took as the measure of work a force operating through a given 
space and proved the principle of the transmission of work. 
This principle, work = Eds, is the ground of the energy con¬ 
ceptions, and from it comes the theorem of the mechanical 
equivalence of heat and work. Robert Mayer , 1842, laid down 
these concepts: “ Energy is indestructible; ” “ energy has 
variable manifestations; ” “ energy is imponderable.” He 
also distinguished clearly “ potential and kinetic energy.” 
These concepts have dominated the thought of the past 50 
years, but recently we are trying to do away with the dis- 
