on Mr. HcrnpalJi' s Tlicory. 291 



" If," says C. (Annals for September, page 210), "a hard 

 moving body A strike a hard quiescent body B in the lines 

 of their centimes of gravity, the quiescent body yields to the 

 stroke ; and this it must do, lessening A's motion and increasing 

 its o-jon, until it shall have acquired a velocity equal to that of 

 A." Taking this palpably absurd proposition for granted, 

 which C. proves by saying it is " too self-evident to require 

 further illustration," it manifestly follows, that some time, how- 

 ever short it may be, is required for the accomplishment of 

 these ^^ yields to the stroke" " until it shall have acquired" &c. 

 During this time, therefore, as each of the bodies C. tells us 

 receives its change " of course not among its parts, but alto- 

 gether," the two bodies have different velocities, though both 

 are continually in contact, and moving one before the other ; 

 and the velocities are differently affected, the one being an 

 " increasing," and the other a decreasing velocity. Surely C. 

 must have something more than common confidence in his skill 

 to prescribe such a dose of absurdity as this for the credulity 

 of the world ! Yet this dose, — absurdity, proposition, or what- 

 ever it may be called, — demonstrated so appropriately and pro- 

 foundly by the luminous assertion that it is " too self-evident 

 to require further illustration," is the base of C.'s fabi'ic of col- 

 lision, — the effort of intellect on which he prides himself over 

 and over, — the magic spell which is to destroy, not merely what 

 Mr. Herapath and D. have wi'itten, but what Wallis, Wren, 

 Huygens, and Newton, have written ! ! Really, should another 

 edition of the Annals be published, I would recommend C. to 

 preface his paper with the following modest effusion of Horace : 



" Nil parvum, aut humili modo. 

 Nil mortale loquar. — " 



Besides the absurd conclusion, that of two perfectly hard 

 bodies in contact the leading one moves slower than the follow- 

 ing, which so obviously and immediately flows from C.'s strange 

 proposition and still more strange demonstration, it would be 

 very easy to exhibit other instances, under different views, 

 ef|ually as absurd and as obvious. For example: we might 

 show, if C.'s proposition be correct, that during the stroke the 

 aggregate momentum of the two bodies, supposed to be in 

 contiict and moving with a connnon velocity, is absolutely less 

 t])an the aggregate momentum before or after the stroke ; be- 

 cause Ijefore the stroke is completed the body B, by C.'s pro- 

 position, " is " continually " increasing its own motion." Here, 

 then, this monstrous conclusion follows, namely, that the ag- 

 gregate motion of the balls both din)inishes and increases of 

 itself during the stroke. Such is the legitimate consecjuence 



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