■292 FOURTH REPORT — 1834. 



ficial stratum in which there is any sensible variation must be 

 exceedingly minute. If that depth may be neglected in com- 

 parison of the radius of sensible activity of the attractive force, 

 Laplace's principles suffice for a theory of Capillary Attraction, 

 without being inconsistent with those of M. Poisson. We may 

 add as a theoretical reason for the supposition of a rapidly 

 decreasing repulsive force united with a feeble and slowly de- 

 creasing attractive force, that we may thus understand how the 

 fluid particles will move readily among each other, retaining 

 the same mean interval ; for there will be a small obstacle to any 

 change of their relative positions by separation, but a great 

 obstacle to any approach within a certain limit*. Perhaps 

 experiments with light, which appears to be the most success- 

 ful instrvmient for searching into the intimate constitution 

 of bodies, offer the best chance of getting at something satis- 

 factory on the delicate point we have been speaking of. In the 

 mean time, while M. Poisson 's theory will engage the attention 

 of the speculative philosopher, there appears no reason why the 

 simpler theory of Laplace should not be made the vehicle for 

 conveying" to the younger students of science, in an elementary 

 form, the explanations of a numerous and interesting class of 

 phjenomena. 



Various causes, which it would be useless to detail, prevented 

 me having a sight of the Number of Poggendorff's Annalen 

 containing the " New Experiments on Capillarity," by H. F. 

 Linkf, (mentioned by Professor Moll at the Meeting of the 

 Association,) till within a short interval before the revision of 

 this Report for the press. I fear that, from want of time and 

 sufficient acquaintance with the German language, the following 

 notice of them will not be such as their importance demands. 



The object of M. Link is to ascertain the comparative ascents 

 of different fluids bj'^ capillary attraction, in a manner that would 

 be free from the sources of error to which the methods of former 

 experiments had been liable. For this purpose he observes the 

 ascent between two glass plates inclined at a small angle with 

 the line of junction vertical, in which case, as we know, the 

 suspended fluid takes the form of a rectangular hyperbola. The 

 instrument he made use of provided for the adjustment of the 



* It will readily be seen, that under these circumstances the fluid would be 

 susceptible of division by a thin plate by the application of a very small force, 

 and we might thus account for a characteristic property of fluids, which, as was 

 mentioned in my former Report (p. 1.33), has been employed as the basis of 

 their mathematical treatment. I was in error in supposing that this method 

 has only been recently proposed ; it appears to have been thought of by Pascal. 



f Annalen der Pliysik und Cheviie, bd. xxix. 1833, p. 401. 



