406 JAMES WATT. 
Numerical valuations make us appreciate so well the 
importance of his inventions, that I cannot resist the de- 
sire to present two more improvements. I borrow them 
from one of the most celebrated correspondents ‘of the 
Academy, from Mr. John Herschel. 
The ascent of Mont Blane, starting from the valley of 
Chamouni, is justly considered as the hardest work that 
a man can accomplish in two days. Thus, the maximum 
mechanical work of which we are capable, in twice twenty- 
four hours, is measured by transporting the weight of our 
body to the elevation of Mont Blane. This work, or its 
equivalent, would be accomplished by a steam-engine in 
the course of burning one kilogram of coal. Watt has, 
therefore, ascertained that the daily power of a man does 
not exceed what is contained in half a kilogram of coal 
(1 Ib. Avs.). 
Herodotus records that the construction of the great 
pyramid of Egypt employed one hundred thousand men 
during twenty years. The pyramid consists of calcareous 
The detent intended to be used in engines having several cylinders, 
will also figure among the projects of the Soho engineer. He suggests 
the idea of perfectly water-tight pistons, though consisting entirely of 
pieces of metal. It was Watt also who first had recourse to mercurial 
gauges to appreciate the elasticity of the steam, both in the boiler and 
in the condenser; who imagined a simple and permanent gauge, by 
the aid of which, and at a glance, the height of the water in the boiler 
can be known; and who, to prevent this Jevel from ever varying to an 
inconvenient extent, connected the movements of the feeding-pump 
with those of a float, which, when required, was placed in an opening 
of the lid of the engine’s principal cylinder, forming a little indicator, 
so combined as to show exactly the law of the steam’s consumption 
relative to the piston’s position, &c. If time permitted, I would show 
Watt not less clever, or less fortunate, in his endeavours to improve 
the boilers, to diminish the loss of heat, and to burn completely the 
torrents of black smoke that escape from common chimneys, however 
high they may be carried. 
