100 UPWARD GROWTH OF THE HEAD, AND pt. rr. 



as the nearness of eacli part to the centre of the wheeL 

 Therefore, gravity would again resume its powers over 

 each part directly as the centrifugal force diminished, 

 and thus should elevate the heads of the plants on the 

 horizontal wheel. This observation will hold good, 

 whatever may have been the degree of centrifugal force 

 applied. I have not, indeed, any idea of the degree 

 which actually was applied ; and it is needless to 

 mention the number of revolutions of the wheels in a 

 given time, since their diameters are not given in either 

 of the two accounts which I liave seen of this most 

 beautiful experiment ; therefore, no correct notion can 

 be formed of the degree of centrifugal force to which 

 each part of the plants was subjected. But, as I have 

 said, in any case the degree of that force must have 

 varied in every part of the plants ; that is, it must have 

 decreased on the stems, and increased on the roots, 

 directly as their growth ; and when the heads of the 

 stems had worked up the stream of centrifugal force to 

 the centre of the wheel, ' where they soon met,' all 

 action of the centrifugal force must have ceased on 

 them ; and had they not turned upward at right angles 

 to the spokes of the horizontal wheel, they would have 

 gone headlono' down the contrary current of centrifuo^al 

 force. 



Sir Humphry Davy remarks on this experiment : — 

 ' These facts afford a rational solution of this curious 

 problem, respecting which different philosophers have 

 given such different opinions ; some referring it to the 



