M. R. Clausius on the Effect of Fluid Friction, ^c. 139 



for the greater part of the observed deviation, it leaves about 

 three-tenths unaccounted for. 



In the account of Mr. Bunt's experiments, contained in the 

 June Number of the Magazine, the observed deviation of the 

 apse for every tenth of an inch of semiaxis minor is given for 

 the pendulum used by him, which was 53 feet in length. 



The observed deviation per tenth of inch semiaxis minor is 

 0*7 of a degree per hour. 



On calculating (14.) for this pendulum, we find 



N=21-46x«^' (17.) 



Substituting in this expression the values 3*5 feet and "1 inch 

 for a and b (as stated in Mr. Bunt's communication), we obtain 



N = 0°-626 (18.) 



In this case the formula agrees more nearly with experiment. 



In Mr. Bunt's communication in the last Number of the 

 Magazine, he states as the result of a new set of experiments, 

 that he found the correction for y^th of an inch ellipticity or 

 semiaxis minor, in a mean arc of about three feet, to be 0°*43 

 per hour. If we apply equation (17.) to this case, the result is" 

 0°'27, which differs much more from observation than Mr. Bunt's 

 former determination of the correction. From all this it would 

 appear, that other causes beside the apsidal motion here con- 

 sidered operate in disturbing the angular motion due to the 

 earth's rotation. 



XXIII. Reply to a Note from Mr. W. Thomson on the Effect of 

 Fluid Friction, ^c, which appears in the June Number of the 

 Philosophical Magazine. By B. Clausius*. 



THE above-mentioned note of Mr. Thomson refers to an in- 

 vestigation of mine on the deportment of steam during its 

 expansion under various circumstances f; and itisstatedinthe note, 

 that although I determine the work executed by the steam issuing 

 from a vessel, I have overlooked the mechanical effect, which con- 

 sists in the circumstance that a certain velocity must be imparted 

 to the steam, and which must be measured by the vis viva of 

 this motion, and that on this account my objections against his 

 reasoning are groundless. I believe, however, that I shall be able 

 fully to establish the views which I have expressed. 



The above mechanical effect was both known to me and taken 

 into account ; and it is only with regard to the force which 

 causes the velocity of the steam at a small distance behind the 



* Communicated by the Author. 



t Pogg. Ann., vol. Ixxxii. p. 263 ; and Phil. Mag. 4th ser. vol. i. p. 398. 



