Mr. Davies Gilbert’s observations on the steam engine. 35 
This mode of working has yet a further beneficial effect. 
The steam, beginning to act with its entire force, imparts the 
requisite velocity, by rapidly overcoming the inertia ; and this 
force diminishing in the latter part of the stroke, allows the 
machine to exhaust the motion imparted, as it tends towards 
its close ; thus also avoiding all violent percussion, which must 
obviously prove most injurious to the machinery, and in other 
respects be a pure loss. 
It would be unfair towards the memory of a very ingenious 
man, were I to omit noticing, that much about the time when 
Mr. Watt introduced this method of using the expansive 
power of steam, a modification of the same principle was 
invented by Mr. Jonathan Hornblower, of Penryn in Corn- 
wall. According to this method, instead of condensing the 
steam after it had passed under the piston, in the working 
cylinder, the steam is allowed to expand itself over a second 
piston in a second cylinder, when it is finally condensed in 
the usual manner ; and if the second cylinder exceeds the 
first in the proportion of 1 -}- x to 1 , the theoretical effect 
will be identical with that produced by the former method. 
But the mode invented by Mr. Watt excels the other in 
simplicity, and causes less friction. 
The second expedient, that of employing steam at an high 
degree of temperature, and consequently of pressure, sug- 
gested itself in the following manner. 
Experiments had shown, that a quantity of heat about 
nine hundred times greater than what is required to raise the 
temperature of a given weight of water one degree of Fah- 
renheit’s thermometer, becomes latent in the conversion of 
that water into steam. That an elevation of temperature to 
