9(5 MR RUSSELL'S RESEARCHES IN HYDRODYNAMICS. 



rope on its supporters ; and when one experiment has been completed, the ar- 

 rangements are thereby made for instantly beginning- the succeeding experiment. 

 The mode was this : A pjTamidal framing (see Plate III. fig. 6.), was raised to a 

 lieight of 75 feet, formed by four logs of pine rising from the comers of a square 

 of 45 feet, and firmly united at the apex, so as to give attachment to two fixed 

 pulleys, and the structure was made rigid by an oblique framing of spars and 

 ropes. This structure was placed on the bank of the sheet of water at the Expe- 

 rimental Station close to the Bridge of Hermiston, from which there extends a 

 line of bank in a straight line of more than 1500 feet in length, which was accu- 

 rately divided by painted rods into equal portions. Through the two pulleys (C) 

 at the top of the framing were passed the two ends of the rope, and fi-om the in- 

 termediate part of the rope, by means of a moveable pulley (D), was suspended 

 the moving weight. The two ends of the rope that had been passed over the pul- 

 leys at the vertex of the pyramid Avere thus brought down to a point (B), raised 

 6 feet above the level of the water, where they were passed through two other 

 pulleys fixed in the pile of masonry forming one of the piers of the bridge. This 

 forms the whole of the apparatus for the application of the moving force. 



The pyramid being placed at one end of the station, the vessel subjected to 

 experiment was brought to the other end, and one end of the rope of the pyramid 

 was brought along the whole length of the station and attached to (E) the bow of 

 the vessel. Horses were attached (A) to the other end of the rope, which was cut 

 short after leaving the pulleys fixed in the masonry. The horses now started, 

 and having first tightened the rope, began to elevate the Aveight towards the top of 

 the pyramid. But the other end of the rope fixed to the bow of the vessel had to 

 sustain a tension in raising the weight equal to the part acted on by the horses, 

 and, in consequence of this action, the vessel would have begun to move at the 

 same time at which the horses began to raise the weight, but the vessel had been 

 previously fixed by the stern-post to the bank, and thus a reaction was obtained 

 to sustain the weight. When, however, the observers in the vessel observed the 

 weight rise to a given height in the p^n^-amid, they withdrew a small catch in the 

 stern fastenings of the vessel, and she immediately proceeded towards the pyra- 

 mid. In the mean time, however, the motion of the vessel allowed the weight to 

 fall towards the ground, which it would have reached when the vessel had moved 

 through a space equal to twice its original elevation, had the horses been allowed, 

 after having raised the weight, to stand still ; but as they were urged to a motion 

 at their end of the rope with the same velocity which the vessel acquired at the 

 other end of the rope, the weight was kept at rest in the air ; or if the horses 

 moved either a little slower or a little faster than the boat, the effect was merely 

 to allow the weight to ascend or descend in the p}Tamid with a velocit}^ equal to 

 half the difference of the velocities of the horses and the vessel, and thus the dif- 

 ference of the action of the horses was not sensible in the force acting on the 



