256 FOURTH REPORT — 1834. 



quantity of fluid raised being proportional to the raising peri- 

 phery, and consequently to the radius, and being proportional 

 also to the product of the height and the square of the radius, 

 it follows that the height is inversely proportional to the radius. 

 This reasonhig is not incorrect, but defective, as we shall pre- 

 sently see. In a postscript to his paper. Dr. Jurin intimates 

 that the principle of his explanation was not unknown to New- 

 ton and Machin, who, however, do not appear to have sup- 

 ported their views by like experiments. He says also, that the 

 same two mathematicians suggested to him that what he calls 

 the periphery of the concave surface of the tube, is in reality 

 ** a small surface whose base is that periphery, and whose height 

 is the distance to which the attractive power of the glass is 

 extended." It is sufficiently evident that the theory of capil- 

 lary attraction had engaged the attention of Newton, from 

 the 31st query in the last edition of his Optics, which was pub- 

 lished a short while previously to the reading of Jurin's paper. 



In this 31st query, Newton is speculating respecting the na- 

 ture of molecular forces, to which he is of opinion that chemical 

 combinations are owing. In proof of the existence of such 

 forces, he appeals to several instances of attraction of the kind 

 which it has been agreed to call capillary attraction or cohesion. 

 One veiy singular instance is the suspension of a column of 

 mercury in a barometer tube, to more than double the height at 

 which it usually stands, by its adhesion to the top of the tube, 

 which it leaves only by being considerably shaken. Of the 

 same kind with this phaenomenon, Newton considers the rise of 

 water between two parallel plates of glass held at a very small 

 distance from each other and dipped in the fluid. The height 

 to which the water rises, he says, " will be reciprocally propor- 

 tional to the distance [between the plates] very nearly ; for the 

 attractive force of the glasses is the same, whether the distance 

 between them is greater or less, and the weight of the water 

 drawn up is the same, if the height of it be reciprocally propor- 

 tional to the distance of the glasses." This explanation, though 

 true, does not prove that Newton had formed anj^ very distinct 

 idea of the extent of action of the attractive force of the glass, 

 and the mode in which the water is influenced by it. He asserts, 

 moreover, that the height to which water rises in a slender glass 

 pipe, will be reciprocally proportional to the diameter of the 

 cavity of the pipe, and will equal the height to which it rises 

 between two planes of glass, if the semidiameter of the cavity 

 of the pipe be equal to the distance between the planes, or there- 

 abouts." These are not, however, theoretical deductions, but 

 the results of experiments made before the Royal Society. 



