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LV. On the Reality of Force. By Walter R. Browne, M.A., 
M. Inst. C.E., late Fellow of Trinity College, Cambridge*. 
THE Royal Society of Edinburgh have lately published 
the first part of an Essay on the Laws of Motion by 
Professor Tait, F.R.S.E. This essay is a further development of 
the views upon Force and upon the proper mode of presenting 
the principles of Mechanics, which are set forth in the article 
on Mechanics by the same author in the new edition of the 
Encyclopcedia Britannica. Their appearance in such a pub- 
lication, together with the weight attaching to the name of 
their author, is sure to give to these views great currency and 
authority; and I trust therefore it will be considered only 
just that they should be submitted to careful but fearless 
criticism. 
The main point of difference between Prof. Tait and pre- 
vious writers on Mechanics is the view which he takes of Force. 
Force he takes to be a mere expression, an abridged notation 
for some such words as " the time-rate of change of mo- 
mentum," having no real or objective existence whatever. 
Accordingly it should be possible, and is even desirable, to 
expound the whole of Mechanics without introducing this 
word at all, and so without giving the student a chance of 
mistaking it (as he is certainly prone to do) for the symbol 
of a real existence. In preparing his article for the Encyclo- 
pcedia, however, Prof. Tait found it difficult to make this 
desirable change; and accordingly that article proceeds on the 
old lines until it arrives at the last chapter, where the new 
discovery is set forth and expanded. In his recent paper 
Prof. Tait proposes to supply this defect, and to give a sort 
of outline of a new Principia, in which the term Force is 
absent, and replaced by the purely abstract conception which 
is its only proper signification. 
I shall not criticise this first instalment of the work, only 
remarking that, before studying the laws of motion, the stu- 
dent will apparently have to master such conceptions as those 
of Potential Energy, Conservation of Energy, Quaternions, 
Vectors and Scalars, the Principle of Least Action, &c. I am 
thankful, at least, that I was myself taught Mechanics before 
its text-books were constructed on the new principle. But the 
new treatise will not need much discussion if its raison d'etre 
(the non-objectivity of Force) is shown to be erroneous; and 
it is this point to which I wish to address myself. 
Turning to the article " Mechanics " in the new Encyclo- 
* Coimmuiicated by the Author, 
2E2 
