36 JOURNAL AND PROCEEDINGS. 
empty space, something like a heap of sand in a vacuum. Ber- 
noulli pointed out that such a heap of invisibles and whose grains 
were endowed with the property. of mutual repulsion, would re- 
semble air in occupying all accessible space and in pressing against 
the walls which hindered its expansion: as an alternative to this 
assumption of the otherwise unknown ‘‘negative gravity ” he sug- 
gested that the same phenomena might be accounted for by sup- 
posing the gas particles or ‘‘ molecules ” (literally ‘‘ little heaps ”) to 
be endowed with rapid motion, it can easily be seen that the 
pressure caused by the bombardment of these bodies against the 
walls containing them would be cae¢. par. greater the more of them 
there were in a given space, and Bernoulli actually succeeded in 
shewing that ‘‘ Boyle’s law” would hold for a gas built on this plan, 
by means of a mathematical investigation of the properties of a 
system of (perfectly elastic) bouncing balls. 
Of these alternate hypotheses the latter only has proved cap- 
able of further development, and under the name of the “ Kinetic 
Gas Theory” (from a Greek word signifying motion) has played a 
great part in the physics and chemistry of the present century. 
Important as this theory was destined to become at a later date, 
for almost one hundred and twenty years it remained practically 
without fruit, most people finding it easier to take for granted the 
simple relationship discovered by Boyle than to accept the existence 
of a devil’s dance of unseen molecules offered as its explanation. 
During this time however the increased use of machinery was daily 
attracting its owners’ attention to the fact that wherever two parts 
of a machine rub together they are apt to get hot; this formation of 
heat by friction, though familiar enough to-day, seemed then so 
strange that at the beginning of this century the King of Bavaria, 
his minister, Count Rumford, and a score of notables, watched for 
over two hours, with ever increasing interest, the signs of heat gen- 
erated by grinding a blunted borer against the metal of an unfinished 
cannon in the Arsenal at Munich, and when some water placed in 
the cannon tube finally began to boil their astonishment and delight 
knew no bounds, Letters were at once despatched to England (where 
Sir H. Davy had been for some time engaged in similar work) and 
elsewhere, informing the world of this wonderful experiment, which, 
once fully confirmed and rightly interpreted, was fated to overthrow 
the ‘ material’ theory of heat, till then generally accepted. 
