ON A NEW CURRENT-METER. 165 



way down, and also in order that the apparatus may hang 

 perpendicularly and inimovable without being disturbed by (he 

 current. 



Near the upper end of the frame, the compass-box, d, is 

 placed, and beneath it the pendulum is suspended by a linen 

 thread. For the purpose of retaining the pendulum in case of the 

 thread breaking, a head, e (Fig. 3), is screwed on at the upper 

 end of the pendulum, by means of which the pendulum, in such 

 a case, would continue to hang to the protecting pocket, /". This 

 head has also another purpose, which shall be mentioned. 



The wings, g, by which the pendulum acquires a surface of 

 about 160 sq. cm. to present to the current, hold between 

 them the bob of the pendulum, h, an ordinary glass float of the 

 kind generally used by Norwegian fishermen. The pointed end 

 of the pendulum is attached to the wings. The sliding weight, 

 i, is of lead poured into a brass case, and weighs 150 grammes. 

 For more rapid currents, when this weight is not sufficient, an 

 extra lead, weighing 612 gr., is put outside it. It forms a mantle 

 round the smaller weight, and has a groove along one side, so 

 that it can be easily slid on to the narrower pendulum-rod. 



Just beneath the point of the pendulum is a flat, spherical 

 cup, k, with its centre of curvature in the pendulum's point of 

 suspension, and this serves both to arrest the pendulum, and as 

 a scale for the reading of its displacement. For this purpose it is 

 fined inside with a thin layer of cork, graduated for every second 

 point of the compass, and with concentric circles with radii of 

 1, 2, 3, etc. up to 11 cm. A barrier prevents the point of the 

 pendulum from coming beyond the platform. The arresting is 

 effected by the raising of the platforai, and its being pressed 

 against the point of the pendulum; the mechanism of this will 

 be best understood from the drawings (Figs. 1 & 2). In fig. 1 

 the pendulum is still free; fig. 2 shows the arresting mechanism 

 after the apparatus has been stopped. The messenger, m, opens 

 the hooks, n, n, thus releasing the levers, p, p, which, by the 



