il4 On the Measure of 
still ignorant of the properties of the balance 
regulated by springs. If Smeaton had not 
availed himself of just. theory, as well as ex- 
periment, we might still have had to learn the 
"principles by which we must be guided in 
applying water to the best advantage as a 
moving power. If a clear and strong under- 
standing, and a mind richly stored with 
scientific attainments, had not been combined. 
with wonderful fertility of invention, in the 
justly celebrated improver of the steam- 
engine; incalculable labour might still have 
been wasted in performing operations which 
are now accomplished with as much ease and 
regularity as the gentle motions of a time- 
piece. 
But if it were even granted, that all these 
distinguished men might have attained their 
objects without the aid of theory ; it must still 
be acknowledged, that to those who have to _ 
follow their steps, and to apply their inventions 
and improvements to various purposes, under 
various circumstances, it must be of essential 
importance to be free from perplexity in the 
principles by which they must be governed ; 
_ and it is under this impression that L have been 
induced to state to this society some of the 
difficulties which have occurred to myself, in 
common, I believe, with many other practical 
