PROCEEDINGS. 
589 
of its recognized senses: as a physical term to express a fundamental con¬ 
cept of philosophy, and a basic fact of observation, as the force of gravity, 
the force of cohesion, the force of elasticity, the force of magnetism, the 
force of affinity, the force of inertia, or as a mathematical term to express 
mere kinetic relations. In the vernacular, it is the mere synonym of 
power. 
Mr. M. H. Doolittle had previously defined a force as “ that which does 
anything whatever; ” but this definition may require interpretation. A 
chord subtends an arc, though there may be difference of opinion as to 
whether the chord can properly be said to do anything. It is supposed 
that no one regards a mathematical line as a force; but perhaps every 
possible definition would itself need to be defined, and he would not now 
attempt to improve the definition which he had given. The word should 
be so understood as to adapt it for use in fundamental propositions, such 
as that of the “ parallelogram of forces,” and the definition should there¬ 
fore be broad enough to cover every case. He read an extract from 
Newton’s Principia (Book I, sec. II, prop. 1), in which the parallelogram 
of forces is made to cover the case in which vis insita, (inertia) is one of the 
forces. He read another extract from the same work (Scholium between 
definitions and axioms), in which Newton speaks of “ the forces which are 
the causes and effects of the true motions.” A body may be conceived as 
voluntarily endeavoring to move in one direction while impelled by an 
external force in another direction. In order to bring this case under the 
general proposition, voluntary effort must be regarded as a force. Some 
writers on physics define force as “ that which changes or tends to change 
a body’s condition of rest or of uniform motion in a right line,” maintain¬ 
ing that a body left to itself perseveres in such a condition, and that no 
force is required for such perseverance; but it may well be doubted, if 
not denied, that any one knows what matter does when left to itself. The 
uneducated usually think that force is necessary to keep a. body from 
falling, but not to make it fall. There are those who maintain that matter 
is always left to itself and produces all the phenomena of the universe 
without foreign assistance or intervention; others hold that matter is 
never left to itself, and that divine or other external force is always re¬ 
quired to keep it in any state of motion or even of existence; between 
these extremes there may be a great variety of opinions, and all are un¬ 
scientific. There is a conservative force which always tends to preserve 
an existing condition of rest or of uniform motion in a right line, and 
there are various mutative forces which in various ways permanently 
or transiently tend to change such conditions. Whether any or all of 
these forces consist of matter itself, are inherent in it, or are impressed 
upon it, are metaphysical speculations which should not be imbedded in 
the significations of terms employed in physical science. We need broad 
terms for broad propositions as well as narrow terms for narrow proposi¬ 
tions ; it is much easier to introduce a new narrow term when it is wanted 
than to replace a broad term that has been spoiled; and those who give 
