FUNCTION OF CRITICISM IN ADVANCEMENT OF SCIENCE. 353 
ton’s three laws of motion. Herein the law of rank is su¬ 
perbly realized, and its crown, universal gravitation, is 
destined to endure at the head. 
Another point that puzzled men so long was, How can a 
body keep moving about another continuously without some 
additional force to sustain the motion in its path? Only 
gradually did the great truth emerge, through the sugges¬ 
tions of Leonardo da Vinci, Galileo’s law of falling bodies, and 
Huyghens’ theory of central forces, till Newton was able to 
define it in the laws of inertia, composition of forces, and 
mutual action. The splendor of these conceptions excited 
the imagination of the best minds, not only to extend the 
sphere of observation but also the purely mathematical analy¬ 
sis of all sorts of mechanical problems. The great contribu¬ 
tion of La-place, d’Alembert, Lagrange, Hamilton, and many 
astronomers, whose names are immortal, have certainly car¬ 
ried out the promise of Newton’s laws to splendid fulfillment. 
Along with the success attending these achievements, there 
grew up the conviction that the entire range of phenomena 
in the universe, great and small, can be finally reduced to 
some part of the theory of mechanics. With this object in 
view, all problems in physics, in chemistry, and even in men¬ 
tal psychology, have been attacked along the lines of mathe¬ 
matical mechanics. What shall we now say—with success ? 
That is the very question to which I desire to direct your 
attention. 
Along with the satisfactory solution of many problems 
which, though great in themselves, are only minor parts of 
a more comprehensive subject, the human mind has grad¬ 
ually gone onwards from the study of the operations of na¬ 
ture, as embodied in certain laws, to an investigation-of what 
is behind the law itself—the forces, the energy, the ultimate 
substance, out of which the material world is built. For if 
the law of gravitation is known, what about the gravitating 
force itself—its origin, nature, and operation ? What about 
molecular and chemical forces in themselves ? What about 
the nature of heat energy, kinetic and potential energy, work 
51—Bull. Phil. Soc., Wash., Vol. 13. 
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