136 On the Measure of 
nature of matter, and that they are the only 
facts which the science of mechanics borrows 
from experience. 
It may be proper to observe here, that M. 
Laplace adopts as first principles, only the two 
first of Sir Isaac Newton’s laws of motion. 
It is surprising that so many different opini- 
ons on this subject should still be held, and it 
is not easy to understand how so many good 
reasoners have, from the same data, drawn 
conclusions so much at variance with each 
other. 
Fifty years ago, M. D’Alembert, speaking 
of the science of mechanics, observed, “that 
“En général, on a été plus occupé jusqu’a 
présent 4 augmenter l’édifice qu’a en’ éclainer 
Ventrée; et on a -pensé ‘principalement: a 
l’élever, sans donner a sés fondemens toute Ja 
solidité ‘convenable.’’* 
No one will deny, that, during the last fifty 
years, great advances have been made in 
the application of mechanical principles to the 
investigation of the motions of the heavenly 
bodics. But as far as these principles have 
been adapted to practical uses, may not) M. 
D’ Alembert’s observation be with seme justice 
applied to the present state of mechanical 
science? or may it not be said, that, not only 
* Tyaité de Dynamique, Discours prelim. p. 4. 
