74 DISSERTATION SECOND. [part t. 



reduced to a slender ring of water which goes all round 

 the vessel, and this, though now so inconsiderable, has. 

 the property of being independent of the size of the vessel, 

 so as to be in all cases the same when the materials are 

 the same. As there can be no doubt that this ring pro- 

 ceeds from the attraction of the sides, and of the part im- 

 mediately above the water, so there can be no doubt that 

 the capillary suspension, in part at least, is derived from 

 the same cause. An effect of the opposite kind takes place 

 when a glass vessel is filled with mercury. 



V. Next to these may be placed what are called instan- 

 tiae manipulares, or collective instances, that is, general 

 facts, or such as comprehend a great number of particular 

 cases. As human knowledge can but seldom reach the 

 mosl general cause or form, such collective instances are 

 often the utmost extent to which our generalization can 

 be carried. They have great value on this account, as 

 they likewise have on account of the assistance which 

 they give to farther generalization. 



Of this we have a remarkable instance in one of the most 

 important steps ever taken in any part of human know- 

 ledge. The laws of Kepler are facts of the kind now 

 treated of, and consist of three general truths, each belong- 

 ing to the whole planetary system, and it was by means 

 of them that Newlon discovered the principle of gravita- 

 tion. The first is, that the planets all move in elliptical 

 orbits, having the sun for their common focus ; the next, 

 that about this focus the radms vector of each planet de- 

 scribes equal areas in equal times. The third and last, that 

 the squares of the periodick times of the planets are as the 

 cubes of their mean distances from the sun. The know- 

 ledge of each of these was the result of much research, and 

 of the comparison of a vast multitude of observations, in- 

 somuch that it may be doubted if ever three truths in 



