ELECTRICITY. 



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clock, so that all that is necessary to keep the 

 clocks working is simply to wind up regularly 

 the going clock, and the sympathetic clocks 

 will for any length of time always keep precise- 

 ly the same time as it. 



Automatic Registration of Earthqualce- 

 Shocks. At the observatory on Mount Ve- 

 suvius, Prof. Palrnieri has arranged a seis- 

 mograph for the registration of earthquake- 

 shocks. The object of the instrument (says a 

 writer in Nature) is twofold : first, to measure 

 the direction and intensity of a shock ; second, 

 to record the history of an earthquake. The 

 shock may be either vertical or horizontal, or 

 partly vertical and partly horizontal. For the 

 vertical shocks a fine metallic point is sus- 

 pended by a coil of wire over a cup of mer- 

 cury, the coil acting as a spring, and the 

 slightest upward motion of the earth is suffi- 

 cient to cause the point to dip into the mer- 

 cury. This completes a galvanic circuit, which 

 stops a clock at the exact half-second at 

 which the shock occurred, and rings a bell to 

 call the observer. There are three or four 

 helices of iron of different strengths, which 

 support small magnets above a cup of iron fil- 

 ings. When a vertical shock occurs, some of 

 these magnets dip into the iron filings, and a 

 light index attached measures the intensity of 

 the shock. For horizontal shocks there are 

 four glass tubes. Each of them is bent twice 

 at right angles, so as to form a U-tube. One 

 arm of this tube has more than double the 

 diameter of the other, and is shorter. The 

 four tubes point in the directions of the four 

 cardinal points. Each tube has a certain quan- 

 tity of mercury pourqd into it, and on the sur- 

 face of the mercury, within the narrow arm 

 of the tube, there rests a small weight attached 

 to a silk fibre, which passes over a delicate 

 ivory pulley, and has a counterpoise attached 

 at the other end. Each pulley has an index 

 and circular scale to mark the angle turned 

 through. The extremity of a wire is fixed at 

 a small distance above the surface of the mer- 

 cury in each tube. If then a horizontal shock 

 occur, the mercury rises in the corresponding 

 tube; but it rises higher in that one which 

 has its long arm to the north. The pulley is 

 turned through a certain angle, which is 

 measured by the index, and at the same time 

 the mercury in rising comes in contact with 

 the fixed wire, and so completes a galvanic 

 circuit which rings a bell, and stops the clock 

 at the exact half-second when the shock 

 occurred. If the shock comes from some in- 

 termediate point two of the indices will be 

 moved, and the direction and intensity can be 

 measured by observing both of them. We 

 have seen up to this point that the instrument 

 will measure the direction and intensity of a 

 shock, will mark the time at which the shock 

 occurred, and will ring a bell to attract the 

 attention of the observer on duty, who may 

 register succeeding shocks, or, if the earth- 

 quake has ceased, may reset the apparatus. 



But this is not all. The galvanic circuit, which 

 is completed at the moment a shock occurs, 

 releases at the same instant the pendulum of a 

 second clock, which has been held out of the 

 vertical by means of a detent. This clock 

 allows a roll of paper to be unwound off a 

 drum, as in any registering telegraph, at the 

 rate of three metres an hour. A pencil rests 

 nearly in contact with the strip of paper. It 

 is connected with one arm of a lever, the other 

 arm of which' is slightly distant from an 

 electro-magnet. As often as the current passes, 

 this end of the lever is attracted to the mag- 

 net, and the pencil in consequence is made to 

 press on the paper, to be released only when 

 the current ceases. By this means then a 

 continuous history of the earth's trembling is 

 registered, a pencil-mark corresponding to a 

 time of trembling, and a blank space to a pe- 

 riod of cessation. This instrument is extreme- 

 ly delicate, and registers motions of the earth 

 which are too slight to be perceptible to the 

 human frame. While inspecting it some one 

 happened accidentally to touch the casing 

 of the instrument. The alarm was immediate- 

 ly given by the bell, and the two clocks were 

 respectively checked and put in motion by the 

 galvanic current. 



The Magnetic Counter. This is an instru- 

 ment, invented by Mr. Wheatstone, for the 

 purpose of counting and registering the peri- 

 odical motions of any machine, whether ro- 

 tary or oscillatory, and doing a variety of other 

 enumerating work. The counting apparatus 

 is the same as that used in ordinary me,chani- 

 cal registers, but is less liable to get out of or- 

 der, and cannot be tampered with by persons 

 in charge of the machine, and gives its indica- 

 tions at any point however distant. No vol- 

 taic battery is employed, the electric currents 

 being produced by a small piece of iron at- 

 tached to the moving part of the machine, work- 

 ing upon the poles of a magnet. Among the 

 purposes to which this register has been ap- 

 plied are these : To count the number of im- 

 pressions produced by any printing-machine ; 

 also the number of revolutions of the screw 

 or paddle-wheels of a steamship ; also the 

 number of visitors who enter any public place. 

 By its use the rate of working of any number 

 of machines may be seen and compared by the 

 overseer in a distant apartment. 



The Electric Telltale. Various plans have 

 been devised to keep record of the movements 

 of night-watchmen, with a view of insuring 

 the faithful performance of their duties. Most 

 of these have been unsuccessful. M. H. Cau- 

 desy, of Switzerland, has invented an electric 

 telltale, which has been introduced in the 

 Cantonal Penitentiary, at Lausanne, and is 

 found to work well. In the director's room 

 he placed a circular paper dial, having all the 

 hours and minutes marked on it, and revolving 

 by clock-work once in twelve hours. This is 

 electrically connected with knobs (stationed at 

 various points in the rounds made by the 



