THE LAYING OF SUBMAKINE CABLES. 165 



supension frame being altered to receive it, though not as 

 regards the external dimensions. The strip has a little circular 

 countersink stamped in the centre to receive the mirror, and 

 when in position four little clips cut out of the strip are folded 

 over the mirror to clamp it firmly in the seating. The face of the 

 mirror is then flush with the surface of the strip, the magnet 

 being behind and held as shown in the illustration under a 

 small band cut from the strip. Small lugs are also cut in the 

 strip above and below the mirror, to which the suspension silk 

 is tied. In the important adjustment of balancing the suspen- 

 sion for rolling and pitching (necessary in all marine galvano- 

 meter suspensions) it has been the aim of the designers not to 

 use any shellac for weighting, as this is variable with tempera- 

 ture and Is not satisfactory for hot climates. In the first 

 experiments lead rivets were used for this purpose, put in " plus 

 weight " and scraped down to balance, but in the present form 

 it is found that the front and back weight can be adjusted 

 by bending forward or backward one or both of the sus- 

 pension lugs, and the side weight by moving the magnet to 

 the right or left as required. Weight is also saved by corru- 

 gating the aluminium strip (as shown in the figure), by which 

 exceedingly thin strip can be used ; and the total weight of 

 the mirror, magnet and strip is thus reduced to less than 

 three grains. 



The late Mr. R. Tonking further improved the arrangement 

 by enclosing the whole suspension frame and spring in an air 

 and dust-tight case. This is of brasp, with a circular glass window 

 opposite the mirror, recessed also at the back to accommodate 

 the countersink for the same, and can be slipped into the 

 instrument or withdrawn without fear of the mirror catching 

 and damaging the suspension. Discharges can also be readily 

 observed, with, of course, the usual precaution in damped 

 instruments, of reproducing the same throw in the two 

 capacities compared. There is practically no creep, and the 

 suspension acts remarkably well for speaking purposes. It 

 supplies a simple and ready means of making the ordinary 

 marine galvanometer a dead-beat instrument, without impair- 

 ing its figure of merit, in fact rather improving it. A first or 

 second minute reading can be obtained on a two or three naut 

 length of core so that the electrification can be proved, while 



