854 Sir John Lubbock’s Address. 
the work done in compressing the air, he obtained a numerical 
value of the mechanical equivalent of heat. There was, how- 
ever, in these experiments, one weak point. The matter oper- 
ated on did not go through a cycle of changes. He assumed 
that the production of heat was the only effect of the work 
done in compressing the air. Joule had the merit of being the 
first to meet this possible source of error. He ascertained that 
a weight of 1 1b. would have to fall 772 feet in order to raise 
the temperature of 1 lb. of water by 1° Fahr. Hirn subse- 
quently attacked the problem from the other side, and showed 
that if all the heat passing through a steam-engine was turned 
into work, for every degree Fahr. added to the temperature of 
a pound of water, enongh work could be done to raise a weight 
of 1 1b. to a height of 772 feet. The general result is that, 
though we cannot create energy we may help ourselves to any 
extent from the great storehouse of nature. Wind and water, 
the coal-bed and the forest, afford man an inexhaustible sup- 
ply of available energy. 
It used be considered that there was an absolute break 
between the different states of matter. The continuity of the 
gaseous, liquid and solid conditions was first demonstrated by 
Andrews in 1862. 
Oxygen and nitrogen have been liquefied independently and 
at the same time by Cailletet and Raoul Pictet. Cailletet also 
succeeded in liquefying air, and soon afterwards hydrogen was 
liquefied by Pictet under a pressure of 650 atmospheres, and 
a cold of 170° Cent. below zero. It even became partly 
solidified, and he assures us that it fell on the floor with “ the 
shrill noise of metallic hail.” Thus then it was shown exper!- 
mentally that there are no such things as absolutely permanent 
ases. 
The kinetic theory of gases, now generally accepted, refers 
the elasticity of gases to a motion of translation of their mole- 
cules, and we are assured that in the case of hydrogen at 
o) 
the obscurity more or less complete. If indeed we could use 
the blue rays by themselves, their waves being much shorter, 
