On the Resistance of Fluids. 365 



true, unequivocal measure of mechanical power really expended, 

 or the mechanical effect actually produced." Now I freely and de- 

 liberately incur whatever of responsibility there may be in affirming 

 that this is a most egregious error: and that momentum is never a 



O O 7 



measure of power in the mechanics of engineering and the arts. I 

 know that on this error much of the theory of mechanics is based ; 

 and I repeat that so far as it is thus based " it must be given up" 

 It is this error pervading treatises of mechanics which has rendered 

 them worse than useless as guides to practical men on subjects rela- 

 ting to the application and use of mechanical power. The doctrine 

 of the " maximum effects of machines" owes its origin entirely to 

 this error ; a doctrine so absurd that if a mere tyro in practice were 

 to construct machinery on the principles there recommended, he 

 would render himself ridiculous among practical men. 



Let it not be imagined that I would promote what Prof. K. calls 

 the " hostility of theoretical and practical science." 1 seek a re- 

 conciliation between them on the only ground on which permanent 

 peace can be established ; — the purgation of the theory from this 

 grand error. When this is effected, I pledge myself as a friend to 

 both, that all the other errors which Prof. K. admits to exist, shall 

 not seriously interrupt their future harmony. 



Prof. K. concludes his strictures with the following very just re- 

 mark : " and above all, if the accuracy of the demonstrations and 

 conclusions of such minds as Newton's must be impeached, let it be 

 done, I will not say timidly, but cautiously, and with respect." I 

 am not aware that in the article referred to I impeached the demon- 

 strations or conclusions of Newton. I imagine that the points which 

 I called in question, were rather inferences illegitimately drawn by 

 others from Newton's reasonings. However this may be I intended 

 to state my views in a respectful manner. I certainly dicHt with 

 great caution, and not without having first established in my own 

 mind a perfect conviction of their truth. If therefore I have actu- 

 ally arrayed myself against Newton I shall not retreat, nor seek re- 

 fuge behind any name, but take my stand upon the immutable laws 

 of nature. If these will not sustain me let me be put down. 



In conclusion I will only remark, that if my former communication 

 appeared to Prof. K., as would seem from the paragraph last quoted, 

 to lack that modesty which ought to characterize the production of 

 one who can make but little pretension to mathematical knowledge, 

 in comparison with the distinguished men who have before written 



