Velocity of Transmission of Disturbances through Sea-water. 501 



The tuning-fork — one of Koenig's — making, or rather marked as 

 giving, a hundred vibrations per second, was maintained electrically 

 by a second battery. The scribing apparatus, consisting of two 

 scribers and two electromagnets, could be adjusted through a con- 

 siderable range in a vertical plane, and in a plane perpendicular to 

 the motion of the pendulum ; and also to some extent in a plane 

 parallel to the plane of motion of the pendulum. There was a good 

 deal of trouble about this part of the apparatus, chiefly resulting 

 from the desire we bad to lose no sensitiveness through slowness of 

 action. To this end the levers of the scribers were made of aluminium, 

 and the magnets and springs were very powerful as compared with the 

 moment of inertia of the scribers around their axes. We altered this 

 apparatus, almost remaking it several times, as we found that the 

 limit to the accuracy of our time observations lay in the discrimina- 

 tion of the precise point at which the straight line, traced by the 

 scriber at rest on the smoked glass, began to be interrupted by the 

 motion of the scriber. The sharper the bend the more accurate the 

 discrimination. Finally we got the scribers to break the line with 

 almost complete suddenness, i.e., at something like 90° to its original 

 direction. 



The trigger for firing the charge was of a kind that will easily 

 occur to the reader. The catch on the pendulum could be slightly 

 set forwards or backwards, and only affected the trigger when the 

 pendulum was moving in one direction. The trigger itself could be 

 moved along on an arc below the pendulum, so as to allow the firing 

 to take place at such a time as would give the scribers the benefit of 

 the pendulum's most rapid motion. In order to ensure a good instan- 

 taneous contact, the trigger on being let off drove (under the influence 

 of a powerful spring) a platinum-coated wedge between the opposing 

 faces of the brass interrupting plugs. The firing battery consisted of 

 six good bichromate elements with large plates ; and the battery for 

 the recording gear consisted of twenty Leclanche cells, ten with large 

 plates and ten with small. In all cases use was made of a good earth 

 "return," this being secured permanently at one end with a bit of 

 armoured cable, at the piles with copper plates, and at the torpedo 

 with a bit of old copper wire or thin plate. 



Receiving Apparatus. — " Gauges." 



This part of the experimental arrangement was the most difficult 

 to get to work satisfactorily. At first a sort of small pendulum was 

 supported so as to hang near an india-rubber disk, inside a wide brass 

 cylinder ; the whole was sunk under water, leaving the contact wires 

 protruding. The difficulties, however, were such as to render this 

 form of apparatus useless. The form finally adopted for very small 

 explosions, mere noises, in fact, is shown in Plate 4. The great 



