the Charges of Mr. O'BTien. 347 



what was only asserted by Mr. Green, viz. that transverse and 

 normal vibrations are in general propagated with different 

 velocities. I have learned since that M. Cauchy had previously 

 arrived at the same result. Professor Kelland distinctly de- 

 nies the correctness of this result in the Royal Edinburgh 

 Transactions, vol. xiv. p. 396." I have not the passage to 

 turn to, but your readers have, and I fearlessly assert, / never 

 denied the correctness qfM. Cauchy* s result. I could not have 

 done so. The assertion, or rather hypothesis, of Mr. Green is, 

 if my memory does not deceive me, a very different affair. 

 But instead of denying Mr. Green's vibration (which he calls 

 normal, but which is really not so), I have adopted, applied, 

 and acknowledged it over and over again. 



I do not intend to touch on every point in Mr. O'Brien's 

 reply. I do not conceive that an acrimonious personal con- 

 test can ever benefit the cause of science. I shall therefore 

 rest satisfied with clearing myself. Had Mr. O'Brien con- 

 tented himself with saying, " I assert that the equations at the 

 foot of p. 162 of the Transactions of the Cambridge Philoso- 

 phical Society are essentially erroneous" &c, " they prove 

 that Mr. Kelland's equations in the Cambridge Philosophical 

 Transactions, vol. vi. p. 159, are essentially erroneous" I would 

 have excused the harshness of the term " essentially erroneous" 

 in italics, and have given the following explanation. It is 

 perfectly possible that these two equations may be written 

 down unaccompanied by the restriction that one of the axes 

 of coordinates is the direction of transmission ; nay more, it is 

 perfectly possible that I have stated that g is not necessarily 

 measured along an axis. The fact is this : all these equations 

 were deduced on the hypothesis that the axis of y is the axis of 

 transmission. 



When the paper was copied for the press (by my friend 

 Mr. Bird) certain interpolations were introduced, which, as 

 1 never saw the proof sheets, remain on the pages. This ex- 

 planation must not be understood as the admission of my 

 having fallen into error further than it states. 



I assert, first, that when it is remembered that one of the 

 axes is that of transmission, all my equations in that memoir 

 are correct ; and secondly, that I never deduced one result 

 from an equation which is not correct, so far as that memoir 

 is concerned. 



Mr. O'Brien's argument that because M.Cauchy's equation 

 is of one form and mine of another, one must be incorrect, is 

 only good when the hypotheses are identical. That they are 

 not stated to be otherwise must be a fault of mine. But I 

 have never employed the equations in this form, to the best of 



2 A2 



