474 POPULAR LECTURES AND ADDRESSES. 



the drawing of it in Scott Russell's paper, three 

 pairs of horses are seen galloping along. They seem 

 to be galloping on air, but are of course on the 

 towing path ; and this remark may be taken as an 

 illustration that, if the horses only galloped fast 

 enough, they could gallop over the water without 

 sinking into it, as they might gallop over a soft 

 clay field. That is a sober fact with regard to the 

 theory of waves ; it is only a question of time how 

 far the heavy body will enter into the water, if it 

 is dragged very rapidly over it. This, however, is 

 a digression. In the very ingenious apparatus 

 of Scott Russell's, there is a pyramid 75 feet 

 high, supporting a system of pulleys which carry 

 a heavy weight suspended by means of a rope. 

 The horses are dragging one end of this rope, 

 while the other end is fastened to a boat which 

 travels in the opposite direction. It is the old 

 principle invented by Huyghens, and still largely 

 used, in clockwork. Scott Russell employed it to 

 give a constant dragging force to the boat from the 

 necessarily inconstant action of the horses. I need 

 not go into details, but I wish you to see that 



