1876.] Currents and Temperature in the Ocean. 327 



dial-plate, a current will circulate from the battery C, through galva- 

 nometer g' g' (the needle of which is deflected), axis of lever cc, lever 1 1, 

 contact N, leading-wire to the contact against the underside of which 

 the platinum wire is pressing, and through it and the pivots of the 

 gimbals to earth E', and back to the battery-pole Z, which must also be 

 put to earth. It is clear that by calling this contact of the dial-plate 

 north, and soldering the other fifteen wires in order to the under sur- 

 faces of the remaining contacts (as in diag. 2. fig. 3), with their other 

 ends attached to the corresponding contacts around the periphery of the 

 ebonite disk (e e) in the instrument below, in order to find the direction 

 of any other current than a northerly one, the handle has only to be 

 moved round the dial until the galvanometer-needle is seen to deflect ; 

 and when this is the case, the lever will be pressing against the contact 

 whose letter represents the direction of the current which was required 

 to be found. This reading having been duly registered, the instrument 

 is lowered some 100 fathoms or more ; and after waiting for a few 

 minutes for the instrument to settle down in the direction of the cur- 

 rent, the handle of the dial-plate is again turned round on board, in 

 either direction, over the contacts until the galvanometer-needle again 

 deflects, showing that an electric current passes ; and after registering 

 the direction of this current also, the instrument may be lowered to 

 greater depths, and readings taken at any points between the surface and 

 the bottom of the sea. On reaching the bottom the weights detach 

 themselves by means of the apparatus (diag. 1. fig. 3) invented by Mr. 

 Edward Hill, and the instrument (whose weight has been previously ad- 

 justed to enable it to float, when there is no sinker attached, and remain 

 in an upright position) offers little weight or strain to the cable when 

 being hauled up. The detaching-apparatus made use of is one designed 

 by Mr. Edward Hill expressly for detaching weights ; and after many 

 trials this method has been found to be exceedingly sure and trust- 

 worthy. So long as the sinker is in mid ocean, the ring r' r' remains 

 tightly hooked on to the apparatus (fig. 3) ; but directly the sinker rests 

 on the bottom and the strain is taken off, the ring r' r' falls, and the 

 form of the apparatus effectually prevents the ring r' r' from rehooking 

 the sinker when the instrument is raised ; instead of which it slides up 

 the curved surface (cf. fig.) and becomes completely detached. The de- 

 taching-apparatus is left at the bottom, after each series of observations, 

 with the sinker ; but as this can be made exceedingly cheaply, the loss is 

 very trivial. 



The cable containing the core of sixteen insulated wires must be 

 strengthened by strands of steel wire ; and it would be well to make the 

 cable with a larger section at the top, and to taper gradually towards the 

 end attached to the instrument below. 



The strands of steel wire are intended to be finally attached to the 

 rings in the eye-bolts u u, and thus take all the strain off the wires 

 forming the core. 



