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362 JAMES WATT. 
new instrument presented essential improvements in the 
mechanical parts, in the regulators, in the method of 
appreciating the power of the wind; but it will excite 
astonishment to learn that its harmonic qualities were 
not less remarkable, and that they charmed professional 
musicians. Watt solved an important part of the prob- 
lem: he arrived at the temperament assigned by a man 
learned in the mystery, in aid of the phenomenon of the 
vibrations then but ill understood; and which he could 
not have dived into, but in the profound though obscure 
work of Dr. Smith,* of Cambridge. 
PRINCIPLES OF THE STEAM-ENGINE. 
I have now reached the most brilliant portion of Watt’s 
life, and also, I fear, the most difficult part of my task. 
The immense importance of the inventions of which I am 
about to treat, cannot be doubted for one moment; but I 
may not succeed in rendering them suitably appreciated, 
without entering into intricate numerical comparisons. 
In order that these-comparisons, if they become essential, 
may be easily seized, I will present you, in the most com- 
pact manner possible, with the delicate notions of physics 
on which we shall have to rest them. 
By the effect of simple changes of temperature, water 
may exist in three perfectly different conditions ; in the 
solid state, in the liquid state, and in the aerial or gaseous 
state. Below zero on the scale of the centigrade ther- 
mometer, water becomes ice; at 100° it rapidly assumes 
the form of gas; in all the intermediary temperatures it 
remains fluid. 
* Dr. Robert Smith’s work, here alluded to, was intituled Harmonics, 
or the Philosophy of Musical Sounds, and printed in 1760. He was also 
the author of the well-known System of Optics.— Translator. 
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