MEMOIR XXVI.] CAPILLARY ATTRACTION, ETC. 343 



plants that liquid is called the sap; in animals, the 

 blood. 



When the distance through which such a liquid has 

 to pass is small, there seems to be little difficulty in as- 

 signing the cause of its movement; but how shall we 

 explain the rise of the sap in the great sequoia-trees of 

 California, some of which attain a height of more than 

 four hundred and thirty feet? To force a column of 

 water to such an elevation would require a pressure of 

 more than two hundred pounds on the square inch. Yet 

 we cannot doubt that the power which overcomes these 

 enormous resistances is the same as that engaged in the 

 most insignificant transudations. 



Even in the case of solid mineral substances the parti- 

 cles are not at rest. Boyle, in his tract on " The Lan- 

 guid Motions of Bodies," has collected several interesting 

 instances. 



He says : " But what is more extraordinary, a gentle- 

 man of my acquaintance had a turquois stone wherein 

 were several spots of different colors, which seemed to 

 him for many months to move slowly from one part of 

 the stone to the other. And having the ring wherein it 

 was set put into my custody, I drew pictures of the 

 spots at different times ; and by comparing several of the 

 draughts together, it evidently appeared that they shifted 

 their places, as if the matter whereof they consisted made 

 its way through the substance of the stone. And as far 

 as we observed, the motion of these spots was exceeding- 

 ly slow and irregular. An experienced jeweller, likewise, 

 assured me that in a few turquois stones he had ob- 

 served two different blues in different parts of the same 

 stone, and that one of these colors would, by slow and 

 imperceptible degrees, invade and at length overspread 

 that part of the stone which the other before possessed. 

 And the same gentleman who lent me the spotted tur- 



