442 Prof. Tait on the Laws of Motion. 
versed effective force w on a particle revolving uniformly in a 
circle is nothing but an old friend — " centrifugal force.'' And 
even this phantom is still of use, in skilled hands, in forming 
the equations for certain cases of motion. 
The chief arguments for ar d against a modern modification 
of the laws of motion are therefore as follows (where we must 
remember that they refer exclusively to the elementary teach- 
ing of the subject, and have no application to the case of those 
who have sufficient knowledge to enable them to avoid the pos- 
sible dangers of Newton's method): — 
I. Foe. Is it wise to teach a student by means of the con- 
ception of force, and then, as it \. ere, to kick down the scaf- 
folding by telling him there is no such thing ? 
II. Against. Is it wise to give up the use of a system, due 
to such an altogether exceptional genius as that of Newton, 
and which amply smlices for all practical purposes, merely 
because it owes part of its simplicity and compactness to the 
introduction of a conception which, though strongly impressed 
on us by our muscular sense, corresponds to nothing objective ? 
Everyone must answer these questions for himself ; and his 
answer will probably be determined quite as much by his 
notions of the usefulness of the study of natural philosophy as 
by his own idiosyncrasies of thought. 
Those who desire that their scientific code should be, as far 
as possible, representative of our real knowledge of objective 
things, would undoubtedly prefer to that of Newton a system 
in which there is not an attempt, however successful, to gain 
simplicity by the introduction of subjective impressions and the 
corresponding conceptions. 
In the present paper simplicity of principle, only, is sought 
for ; and the mathematical methods employed are those which 
appeared (independent altogether of the question of their fitness 
for a beginner) the shortest and most direct. A second part 
will be devoted to simplicity of method, for elementary teaching. 
(1) So far as our modern knowledge goes, there are but 
two objective things in the physical world — matter and energy. 
Energy cannot exist except as associated with matter; and it 
can be perceived and measured by us only when it is being- 
transferred, by a " dynamical transaction," from one portion 
of matter to another. In such transferences it is often " trans- 
formed;" but no process has ever been devised or observed 
by which the quantity, either of matter or energy, has been 
altered. 
(2) Hence the true bases of our subject, so far as we yei 
know, are: — 
1. Conservation of matter. 
