Nov. 2, 1876] 



NATURE 



JB To those acquainted with the difficulties in the way of 

 communicating a uniform impulse to the pendulum 

 through the medium of a train of wheel-work, it has, 

 always been a favourite idea directly to maintain the 

 swing of the pendulum by means of an electric current, 

 but, unfortunately, the thing has not hitherto proved 

 feasible ; apparently it must be taken for granted that 

 the action of an electric current cannot be constantly 

 maintained. 



But although electricity is of little service for keeping 

 clocks going, it has been very successfully employed in 

 controlling them. It is, of course, very much more econo- 

 mical to have inferior clocks than good ones, and what is 

 done in this case is to use one good clock for the purpose 

 of controlling a quantity of bad ones. The nature of the 

 apparatus is in general this : our first good clock and all 

 the others are placed in the circuit of a galvanic battery, 

 and what our first good clock does is to close the circuit 

 and transmit a current at every beat of its pendulum. 

 The passage of an electric current around a coil of copper 

 wire (as you no doubt know) converts it for so long as it 

 passes into a magnet, and this current so transmitted by 

 the clock is employed for such a purpose, and the magnets 

 so formed are constructed to operate upon the pendulums 

 of the controlled clocks and accelerate them if they are 



I I 



Fig 2^j 



lagging, or resist them if tjey should be moving too 

 quickly. 



Electricity is also employed for the purpose of cor- 

 recting the time of a clock, say once a day. In this case 

 the clock which is to be corrected is kept at a slight gain- 

 ing rate. Upon the axis of its escape-wheel is a little 

 finger which revolves with it. At a few seconds before, 

 say I o'clock, the controlling clock, by the transmission of 

 a current, brings down an arm in front of the finger and 

 stops the controlled clock for just so many seconds as it 

 is in advance of the controlling clock ; at i o'clock the 

 arm is raised again, and the controlled and controlling 

 clock start off approximately together. 



Such a controlling clock as is used to transmit a cur- 

 rent, say once a day, is also employed for the purpose of 

 dropping time-balls and discharging guns. The time- 

 ball itself is generally composed of wicker-work covered 

 with canvas, and is wound up by hand to its position a few 

 minutes before the transmission of the current, and held 

 by a hook or detent. Upon the arrival of the current the 

 detent (by what arrangement it is unnecessary to describe) 

 is withdrawn, and the time-ball falls. 



To discharge a time-gun, the current usually passes 

 through a very fine platmum wire, which it makes red- 

 hot. Both with time-balls and guns, and wherever it has 

 heavy work to perform, the current from the clock is 

 employed to close another and much more power- 



ful circuit, the latter being that which operates upon the 

 mechanism. 



Instruments employed for the purpose of registering 

 the passage of short intervals of time are called chrono- 

 graphs. These in the main consist of a cylinder covered 

 around with paper revolving at a uniform rate. The 

 rotation of those employed in observatories is generally 

 controlled by what is called a conical pendulum, that is, a 

 pendulum swinging round in the surface of a cone. Such 

 pendulums are much more sensitive to any slight change in 

 the pressureof the clock-train than ordinary oscillating pen- 

 dulums, and require to be controlled by special apparatus. 

 The pendulum used at Greenwich is so contrived, that 

 when it endeavours to move faster (in doing so, of course 

 swinging out further) it dips little spades into an annular 

 trough of glycerine, and its velocity by this means is 

 checked. 



The operation of the apparatus is the following : — A 

 pin upon the pendulum of the normal sidereal clock 

 presses two weak springs together at every vibration, and 

 so transmits a current. This current, by making an 

 electro-magnet, brings down a striker upon the paper of 

 the revolving cylinder. By an arrangement similar to a 

 screw-cutting lathe, the frame carrying this striker just 

 as the cylinder rotates, travels alongside of it, and the 

 clock-beats are consequently indicated upon the cylinder 

 in the form of a spiral of successive pricks. The mecha- 

 nism attached to the clock is arranged so as to pass no 

 current at the termination of each minute (the sixtieth 

 second), and consequently a blank is left upon the cylin- 

 der, by which anybody can tell when the minute hap- 

 pened. Upon the same frame alongside the first striker 

 is a second, which can be brought down by the observer 

 at anyone of the instruments, by touching a button at his 

 side. His observation is consequently registered upon 

 the barrel alongside the clock-beat, and you have no diffi- 

 culty in determining its precise time of occurrence to the 

 tenth or one-hundredth of a second. 



Similar instruments are employed for determining the 

 velocity of projectiles, but in these the cylinder travels 

 at a much higher velocity, and other means of controlling 

 it are made use of. 



THE ARCTIC EXPEDITION 

 T T will of course be some time ere all the results ob- 

 -*■ tained by the Expedition which has just returned 

 from its year's sojourn on the edge of the ice-blocked 

 Polar Sea can be presented to the public. Enough, how- 

 ever, is known to lead us to believe that abundant addi- 

 tions of the highest importance to our knowledge of the 

 physics and natural history of the Arctic Regions have 

 been made ; and meantime we are able to exhibit in a 

 map the main additions which have been made to Arctic 

 geography. 



The Alert and Discovery^ under Captains Nares and 

 Stephenson, left England in May, 1875. Godhavn was 

 left on July 15, and all seems to have gone well till July 

 30, when, after leaving Port Foulke, the ice was met off 

 Cape Sabine, 78° 41' N., from which point the ships had 

 a constant struggle with the pack to the north end of 

 Robeson Channel. So close was the ice that on every 

 occasion the water channel by which the ships advanced 

 very soon closed behind them, rendering it as difficult to 

 return as to proceed north. On August 25, after many 

 hairbreadth escapes, a well-sheltered harbour was reached 

 on the west side of Hall's Basin, north of Lady Franklin 

 Sound, in lat. 81° 44' N. Here the Discovery was se- 

 cured for the winter, a few miles north of Polaris Bay, 

 which was in sight on the opposite side of the channel. 



The Alert, pushing onward, rounded the north-east 

 point of " Grant Land," but instead of finding a con- 

 tinuous coast-line leading 100 miles further towards the 

 north, as everyone had expected, found herself on the 

 border of what was evidently a very extensive sea, with 



