44 2 Experiment in Velocity of Heavy and Light Bodies. 



diately taken up for regelation, but sufficient falls to the bottom through the 

 fissures to lubricate the glacier, and when frozen to move the ice forward. 



Heat is also produced by the action of the ice moving boulders on the 

 earth. 3 If the mean depth of the lake of Zurich (Fig. i) could be increased 

 half an inch in a year, that lake might have been comfortably excavated in 

 15,000 years, which is certainly less than the glacial period. 



(7) I propose to attempt first to prove to you a new law ascertained by experi- 

 ment on motion of bodies down inclines in constrained motion, and thus to 

 show you how much weight affects and increases motion. This law is most 

 important to my argument. Then I propose to contrast the new experiment 

 on constrained motion with the old experiment of free motion, where bodies 

 fall at one velocity irrespective of their weights, that is in vacuo, without 

 touching any substance of any kind in their fall. This is shown by reversing a 

 glass vessel exhausted of air, and holding a light and a heavy body. 



Bodies of the same size and of different weights also roll at nearly the same 

 velocity down an incline, as we see when the surfaces in contact are so small 

 (as in spheres) that the motion approaches a fall in air, or free motion. 



[These experiments were then successfully performed in the lecture-room, by 

 my son, J. J. Tylor, on a slab (Fig. 4.) Two pieces of ice of the same size and 

 weight, slid at the same velocity. But when one was loaded to eight times the 

 weight, it travelled twice as fast.] 



I have before me an inclined plane of slate twelve feet long, two feet wide, 

 down which pieces of ice of different weight will slide at different velocities, 

 while spheres of the same size but of different weights have much the same 

 speed. 



This new law— of weight increasing the velocity of bodies in constrained 

 motion in a definite proportion or ratio— has an important application upon 

 the subject of my lecture, because it bears on the infinitely greater action of 

 rivers and springs in former times, for the following reason : I find, by calcula- 

 tion, that with twenty times as much rain, rivers may have swollen for a short 

 time to 400 times their present volume, and then have eight times their present 

 velocity, for the increase of velocity is as the cube root of the increase of weight 

 of water flowing. The large currents arising from a very small slope in the 

 surface of the ocean, are due to this law. 4 Ocean water would move with one 

 thousandth part of the slope of a small stream, if the ocean stream is one 

 thousand million times the volume of the small stream. Ancient glaciers 

 travelled many times faster than the present ones down the same slopes, and 

 reached much lower levels in consequence. Modern glaciers are only one-third 

 of a degree below freezing, but older glaciers were probably very cold. 



Certain theoretical consideration as to the effect of pressure in modifying the 

 point of freezing have been accepted without sufficient experiments having 

 been made ; and the present accepted glacial theory has been thus constructed, 

 partly upon observation, and partly upon theory not confirmed by experiment, 



