JoLY — On the Investigation of the Deep-sea Deposits. 259 



90° at the moment of couclusion of the stroke in either direction. This is 

 accomplished by two strong springs, S, S. These are coiled loosely round 

 the valve-rod T. As depicted, this valve-rod is just about to be released, 

 throwing both valves over to the left, and so opening cylinder A to the 

 external water, and cylinder B to the receptacle. The force acting to bring 

 this about is contained in the compressed spring S. The loading of this 

 spring has occurred through the engagement of the plate Q with the fork 

 projecting from the rack, which in turn is moved by the stop attached to the 

 plunger, as already explained. The plate Q is attached at the end of a sleeve 

 c, sliding on the valve-rod. The movement of this sleeve to the left has 

 compressed the spring against the stop «, which is firmly fixed on the 

 valve-rod. This stop has, however, been retained from moving to tlie left by 

 catching on the notched trigger t. When the sleeve is moved yet a little 

 further to the left by the motion of the plunger, the trigger is lifted by the 

 piece «, and the valve-rod released. The spiing is sufficiently strong to 

 rapidly throw over both valves to the left through 90°. A similar action 

 occurs at the other end of the valve-rod when the stroke to the right is being- 

 completed. 



The entrance from valve to cylinder is narrowed to an aperture of about 

 0"06 cms., which is the calculated aperture (assuming the formula F" = 2gli, 

 and a value for the coeflScient of efflux of 0'6) required to confer a velocity of 

 one stroke per second on the engine at a depth of 1000 fathoms. 



This small aperture is conferred by means of a screwed-in nipple, which 

 is not shown in the drawing. Alternative apertures may be substituted 

 according to the depth, their dimensions for a given velocity varying with 

 the sqiiare root of the depth. 



As shown in the drawing, each of the four cylinders is fitted with a 

 valve. These valves are, however, coupled across, so that when both engines 

 are in operation the one valve-rod actuates all four without any possibility of 

 loss of phase. It is evidently possible to work with one valve only, suitably 

 perforated, and connected with distributing tubes. This system, however, 

 although it lessens the risk of leakage, involves trouble in installing the 

 engines, as well as difficulty in locating the single valve. There is much to 

 be said for having two valves only and controlling the auxiliary engine from 

 these. 



The general construction of the drill-sounder is as follows : — The four 

 cylinders already described are installed in a wrought-iron bowl-shaped 

 vessel, shown in vertical section in Plate XX. This vessel, which contains 

 also the receptacles for the spent water, is about 90 cms. in diameter (say, 

 c6 inches), and is constructed of strong boiler-plate. The engines are 



