Page:Science vol. 5.djvu/415

 SCIENCE.

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��by diBpJacing a crayuii, which irates upon a turning cylinder covered nilli a sheet of paper.

The mechsiiiBiti of the electric liilamipter ia very sitiipk. us shown ill G^. 3. The rod which ban the

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��track IB «o arranged (hat It slides up an incliiied plane ever; time it is displaccil, and In bo doing presses upon a spring, which, displacing a button of metal, breaks the circuit. The rod immediately returna to its original position, and the interrupted current re- establishes itself. At each breaking of Ihe current, the wheel-work of tlic recording apparatus, freed for a moment, mores, and makes the crayon advance on the paper. The paper-covered cylinder turns uni- fonnly, the rate of rotation being such as to cause the paper to pass in front of the crayon at the rate o( half a centimetre per minute. On the other hand. the crayon is allowed to move only when the current is intemipied. The crayon progresses at each rup- ture of the current only a constant distance.

After a person has travelled around the track, the paper bears a sinuous line similar to that In (a), Ag. 4. In the diagram the time is scored horizontally, the minute spaces equalling half a centimetre. The internipliona score Ihemsetvea vertically, each upward step showing that the pedestrian liaa gone fifty metres; hence the course (n) corresponds to a march of twelve hundred metres in ttfleen minutes.

��thirty-five seconds. In drawing a line connecting Ihe angles of the sinuous line, we have a simpler expres- sion of the march, as seen in the lines b, r, d, ate, which, by their greater or less inclination, show that the gait has been more or le:-s rapid. The line (I), for liiatance, corresponds to a run of sixteen buii- dreil metres In nine minutes and a half, while (c| cor- responds to a march of seven hundred and Bfty metres in sixteen minutes.

By gathering outlines from liuiirs of marching, we have mucli more interesting records, in which llie effects of fatigue are plainly seen, all irregularities in speed being faithfully recorded by the rise or fall of the tine.

The shape of the boot has considerable effect upon the quickness of Ihe march. In order to determine (lie best form of marching-boots, buskins have been mode with lieela which can be regulated, by removing jiiates, so as to be of any height from half a centi- metre to six centimetres. From the experiments it is seen that the quickness of the step increases in proportion to decrease in height of heel. This result tends to an increase in the length of the step, and It is also noticed that the step increases In length and qnickness when Ihe length of the sole considerably exceeds that of the foot. Beyond a certain Umit, however, the precise determinatiou of which can only be made after many experiments, the length of tile sole causes a noticeable fatigue.

The rhythm of the drum ur clarion guiding the steps of soldiers has marked effect upon their speed. Thla problem is very complex. The acceleration of the rhythm may Increaie the speed to the rale of eighty steps per minute; but beyond this the in- creased frequency of the steps causes a slackening in the rale of march. In order to experiment upon this, an electric bell, placed in the centre of the track, is rung by a pendulum, represented above and to the left in fig. I. The rale of ringing can be regulated, and the walker finds It impossible to keep out of step with the strokes of the bell. Starting the bell so aa to cause the man to take forty steps per minute, then gradually making It more rapid, it is seen that Ihe

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��time taken to run a kilometre varies greatly. The length of the steps is simply deducted from the num- ber of oscillations of the pendulum during a tour of the track, whicb represents a well-known course.

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