212 Mr. J. J. Waterston on a Difference in the march 



that is, the motion of rotation is ultimately equal to the angular 

 motion in the orbit, and takes place in the same direction. This 

 is analogous to the moon's motion. 



If a sphere be covered, or partially covered, with water, and 

 made to revolve about a central force, but not necessarily about 

 an axis within itself, the water will be disturbed ; and since it 

 does not attain its greatest elevation instantaneously, the central 

 force will tend to give it a rotatory motion. The motion will be 

 similar to that investigated above, but much more complicated. 

 The motion of a body nearly spherical, and having a large mouu- 

 tain on its surface, will also be similar. 



Rivington, February 8, 1858. 



XXVIII. On the Evidence of a Graduated Difference betioeen the 

 Thermometers of Air and of Mercurtj below TOO" C. derived 

 from M. Regnault's observations on the Tension of Aqueous 

 Vapour. By J. J. Waterston, Esq. 



[With a Plate.] 

 To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



THE comparison between the thermometers of air and of mer- 

 cury made by M. Regnault, and of which an account is given 

 in the Ann. de Chim. vol. v. 3rd series, may seem, from the emi- 

 nent character of the observer, to justify the withdrawal of our 

 confidence from the results of MM. Dulong and Pctit's previous 

 inquiry on the same subject [Ann. de Chim. 1817): nevertheless, 

 before yielding to this conclusion, there is certain evidence in 

 favour of the accuracy of MM. Dulong and Petit's deductions, 

 which appears to me to merit attention, inasmuch as it is derived 

 from the observations of M. Regnault himself in another field of 

 research. Hoping that you may consider the subject of suffi- 

 cient importance, I have drawn up the following paper for the 

 Philosophical Magazine, giving an account of this evidence, and 

 an explanation of the processes of computation by means of 

 which it was obtained. The graphical projection into which the 

 results are cast (fig. 2) enables the proofs of the graduated 

 difference in question to appeal to the eye with but little demand 

 on the attention of the reader. Nevertheless, all the details 

 necessary to enable him fully to check those results will, I trust, 

 be found set forth distinctly and without reserve or bias. 



§ 1. In M. Rcgnaiilt's Etudes sur I'hygrometrie [Ann. de Chim. 

 vol. XV.) we are pi'csented with observations on the tensions of 

 the vapour given by six mixtures of sulphuric acid and water in 

 different proportions, at temperatures ranging between 4° and 



