MOVING FORCi:. 
.17 
to Inve been first suggested to Hook and Ilnvgens, bv their 
practical observation; or. the motion of nendnlir.rts, and '.vj.9 
afterwards adopted by Smeaton, as a rule for the g!t:.t opera- 
tions in whicii lie iiad .so much experience. 
It is much to be regretted, that ihcorv sliculd appear to be at 
variance with practice, or that any ambiguity should remain on 
a (jiiestioii of such general application in mechanics. 
It has ofteti been asserted, indeed, that practical operafions 
need not be afl'ceted by uift'erences of opinion about the mea- 
snie of force ; for, there being no disputed facts, the mere 
scientific explanation of the pitenomena, it is said, can be of 
little importance to pnactical men. 
On this point, however, Mr. Smeaton’s observations merit 
particnlat attention. Ho says, in refetence to mistaken notions 
about tlie measure of force, “ that not only himself and other 
practical artists, but also some of the most approved writers, 
bad been liable to fall into errors, in a|>plyiiig the doctrines 
of force to practical mechanics, by sometimes forgetting or 
neglecting the due regard which ought to be had to collateral 
circumstances. Some of these errors arc not only very con- 
siderable in themselvi*s, but also of great consequence to tlie 
public, as they tend greatly to mislead the practical artist in 
works that occur daily, and w hich require very great sums in 
their execution^.” 
Noiwiiliitanding Mr. Smeaton’s excellent experiments and 
observations on this subject, exhibiting much want of agree- 
ment between the theory usually given, and the praciicai results, 
the m.ch.inical principles of force coruinne to he treated nearly 
as before ; and, I believe, we are not without recem iastauces 
of errors similar to those which he has noticed. 
IMr. Atwoo 1, in his Treatise on the rectilinear motion and 
rotation of Biidies, bestowed considerable attention on Mr. 
Sineaton’s experiments and coneksions. He ako observes, 
that Emerson, and otlior authois of merit, have been led into 
considerable errors, “ by supposing the momentum of bodies 
* i’liilosopliical Transacti >i.*, to'. 66, part id. p. 45U. 
to 
r^piiiions it;- 
tluviicc prac- 
tice. 
a# is well 
stated by 
Smeatou. 
Atwrod’s 
bt.it, mint 
