May 8, 1885.] 



SCIENCE. 



383 



by displacing a crayon, which traces upon a turning 

 cylinder covered with a sheet of paper. 



The mechanism of the electric interrupter is very 

 simple, as shown in fig. 3. The rod which bars the 



Fig. 



track is so arranged that it slides up an inclined plane 

 every time it is displaced, and in so doing presses 

 upon a spring, which, displacing a button of metal, 

 breaks the circuit. The rod immediately returns to 

 its original position, and the interrupted current re- 

 establishes itself. At each breaking of the current, 

 the wheel-work of the recording apparatus, freed for 

 a moment, moves, and makes the crayon advance on 

 the paper. The paper-covered cylinder turns uni- 

 formly, the rate of rotation being such as to cause 

 the paper to pass in front of the crayon at the rate of 

 half a centimetre per minute. On the other hand, 

 the crayon is allowed to move only when the current 

 is interrupted. 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), fig. 

 4. In the diagram the time is scored horizontally, 

 the minute spaces equalling half a centimetre. 

 The interruptions score themselves vertically, each 

 upward step showing that the pedestrian has gone 

 fifty metres: hence the course (a) corresponds to a 

 march of twelve hundred metres in fifteen minutes, 



thirty-five seconds. In drawing a line connecting the 

 angles of the sinuous line, we have a simpler expres- 

 sion of the march, as seen in the lines b, c, d, etc., 

 which, by their greater or less inclination, show that 

 the gait has been more or less rapid. The line (i), 

 for instance, corresponds to a run of sixteen hun- 

 dred metres in nine minutes and a half, while (c) cor- 

 responds to a march of seven hundred and fifty 

 metres in sixteen minutes. 



By gathering outlines from hours of marching, we 

 have much more interesting records, in which the 

 effects of fatigue are plainly seen, all irregularities 

 in speed A being faithfully recorded by the rise or fall 

 of the line. 



The shape of the boot has considerable effect upon 

 the quickness of the march. In order to determine 

 the best form of marching-boots, buskins have been 

 made with heels which can be regulated, by removing 

 plates, 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 

 quickness when the length of the sole considerably 

 exceeds that of the foot. Beyond a certain limit, 

 however, the precise determination of which can only 

 be made after many experiments, the length of the 

 sole causes a noticeable fatigue. 



The rhythm of the drum or clarion guiding the 

 steps of soldiers has marked effect upon their speed. 

 This problem is very complex. The acceleration of 

 the rhythm may increase the speed to the rate of 

 eighty steps per minute; but beyond this the in- 

 creased frequency of the steps causes a slackening in 

 the rate 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. 1. The rate 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 as 

 to cause the man to take forty steps per minute, then 

 gradually making it more rapid, it is seen that the 



Fig. 3. 



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, which represents a well-known course. 



