144 ON MR. EWART’S PAPER ON THE 
nomination, the product of the quantity of a 
pressure by the space through which it acted 
were very strong. It was evident that such a 
measure of effect produced would have a most 
extensive application. 
This measure had been used by Watt to esti- 
mate the effects of steam engines; it had long 
before been adopted by Smeaton ; and writers on 
mechanics had become prepared, both in this 
country and on the continent, for the introduction 
of such a value. It has, therefore, been adopted 
by the most eminent writers on mechanics, both 
theoretical and practical; and without making 
any change in the received definitions of momen- 
tum and moving force, which depend on the mass 
multiplied by the velocity. 
PROGRESS OF THE CHANGE. 
To give some account of the progress of this 
change, which has been gradually taking place for 
a number of years, both in this country and on 
the continent, I shall begin with the former— 
mentioning first Mr. Davies Gilbert, who, in 
1827, gave a paper, in the Philosophical ‘Trans- 
actions, “‘ On the expediency of assigning specific 
names to all such functions of simple elements as 
