ON WAVES. 321 



great magnitude are required, and also when it is desirable to measure accu- 

 rately volumes or forces employed in wave genesis. The same glass plate 

 may be conveniently employed in this case as in the last, only it will now be 

 used in the capacity merely of a sluice, and be supported by two small verti- 

 cal slips fixed to the sides of tiie channel so as to keep it in the vertical posi- 

 tion but to admit of its being raised vertically upwards as atG, PI. XL VII. tig. 2. 

 There is thus formed between the end of the channel G and the moveable 

 plate Pj, a small generating reservoir GP-. This is to be filled to any desired 

 height with water, as from to to P-, and the plate being drawn up, as at P,,, the 

 water of the reservoir descends to lo, the level of the water of the channel, and 

 pushing forward and heaping up the adjacent fluid, raises a heap equal to the 

 added volume on the surface of the water; and this elevation is in no respect 

 sensibly different either in form or other phsenomenon from that generated 

 in the former method, provided the quantity of water added in the latter case 

 be identical with the quantity of water displaced in the former case. 



This method of genesis by fluid column affords a simple means of proving 

 an elementary fact in this kind of wave motion. The fact is this, that while 

 the volume of water in the wave is exactly equal to the volume of water 

 added from the reservoir, it is by no means identical with it. I filled the re- 

 servoir with water tinged with a pink dye, which did not sensibly alter the 

 specific gravity of the water. The column of water having descended as at 

 K, and the wave having gone forward to W^, the generating column remained 

 stationary at K, thus indicating that the column of water had merely acted 

 as a mechanical prime mover, to put in action the wave-propagating forces 

 among the fluid, in the same way as had been formerly done by the power 

 acting by the solid plate in the former case of genesis by impulsion. Thus 

 is obtained a first indication that this wave exhibits a transmission of force, 

 not of fluid, along the channel. 



Genesis by Protrusion of a Solid. — The quantity of moving force required 

 for the wave-genesis may be directly obtained by the descent of a solid weight. 

 The solid at L (fig. 3.) may be a box of wood or iron, containing such weights 

 as are desired, and suspended in such a manner as to be readily detached from 

 its support. Its under surface should be somewhat iminerged. On touching 

 the detaching spring, the weight descends, and the water it displaces pro- 

 duces a wave of equal volume. If the weight and volume of solid thus im- 

 mersed be equal to those of the water in the reservoir in the former case, it 

 is found that the waves generated by the two methods are alike. It is expe- 

 dient that the breadth and shape of this solid generator should be such as to 

 fit the channel, as this removes some sources of disturbance. The results 

 which are produced by this application of moving power are also convenient 

 for giving measures of the mechanical forces employed in wave-genesis. 



This method is especially convenient for the genesis of waves of consider- 

 able magnitude. With this view I erected a pyramidal structure of wood, 

 capable of raising weights of several hundred pounds, over a pulley by means 

 of a crane, and contrived to allow them to descend at will. This apparatus 

 was adequate for the generation of waves in a channel three feet wide ami 

 three feet deep ; and the same construction may be extended to greater 

 dimensions. 



Transmission of Meclianical Power hy the Wave. — By the last two me- 

 thods of genesis there is to be obtained a just notion of the nature of the 

 wave of the first order as a vehicle for the transfer of mechanical power. By 

 the agency of this wave the mechanical power which is employed in wave- 

 genesis at one end of the channel, passes along the channel in the wave itself, 

 and is given out at the other end \\\t\\ only such loss as results fro)n the 



1844. V 



