274 Remarks on the theory of the Resistance of Fluids. 



Art. XIV. — Remarks on the theory of the Resistance of Fluids; 

 by Eli W. Blake. 



TO PROFESSOR SILLIMAN. 



Two of your correspondents, whose communications have appear- 

 ed in recent numbers of the Journal of Science, advocate what they 

 suppose to be different theories in relation to the resistance of fluids. 

 Mr. L. R. Gibbs, (vol. 28, page 135) advocates what he considers a 

 new view of the subject, advanced by Professor Wallace. Professor 

 Keely, (vol. 28, page 318) defends the old theory in opposition to 

 these supposed new views. 



Having bestowed some thought on the subject of the resistance 

 of fluids, and having arrived at conclusions differing essentially from 

 those advocated by either of these gentlemen, and of course, from 

 the usually received theory, a hint at these conclusions, and at the 

 process by which I arrive at them, may not be uninteresting to 

 your correspondents, and perhaps to some other of the readers of 

 the Journal of Science. I say a hint; because for the want of 

 leisure I shall be able at present to do little more than make a few 

 suggestions. 



1 must first premise that the present state of knowledge on the sub- 

 ject does not enable us to take into consideration all the circumstan- 

 ces which combine to constitute the resistance encountered by a 

 body in moving through a fluid; and therefore the conclusions of 

 theory should not be expected to coincide with the results of exper- 

 iment, but should be regarded simply as showing what would be the 

 result of experiment, if the circumstances taken into consideration 

 were the only circumstances tending to modify the result. It is not 

 safe therefore to advocate a theory, as one of your correspondents 

 does, (vol. 28, page 137) on the ground that its conclusions coin- 

 cide more nearly with the results of experiments, than do the con- 

 clusions of other theories; for it is evident from the consideration 

 just stated, that the theory whose results differ most widely from the 

 results of experiment, may nevertheless be the true theory. 



In order that the views which I have to express may be fully ap- 

 prehended, it is necessary that I should remark further, that a great 

 source of confusion and error in Mechanical Philosophy, as treated 

 of in books, is an indiscriminate and ambiguous use of the terms, 

 Power, Force, Resistance, and others of corelative import, to sig- 



