1090
THEORY AND PRACTICE OF ENGINEERING.
Book II.
masses transported, the wheelbarrow as a means of transport is preferable to the crochet ;but it must be remarked that the volume of the masses increases the difficulty of trans-port, and it is probable that hawkers have more fatigue than men at the wheelbarrow.
Coulomb found that to sustain a loaded barrow by means of a dvnanometer, fixedat the point the man holds by, supported a weight of 18 to 20 kilogrammes, andthat the force necessary to drive the barrow loaded on dry firm ground was 2 to 3 kilo-grammes. This weight measures the continuous off;rt of a man pushing the barrow ;multiply this effort by the space, 14 kilometres, which he goes over in 500 journeys, andwe have 28 to 42 great dynamic units for the measure of the efforts which produce theuseful daily effect.
In mines sledges are sometimes used, which slide over an unequal and argillaceous soil;those observed by Gueniveau were drawn by a single man, and loaded with 90 kilo-grammes of coal. The space passed over was 290 metres ; the workman made 24 journeysin the day, and returned with the sledge empty, which gives for the effect in a day 1,0kilogrammes transported 6960 metres, or 626 kilogrammes transported 1 kilometre, aneffect less than that produced by the hawkers, and which was estimated in the precedingarticle at 880.
The small waggons used in mines, says Gueniveau, are supported on 4 wheels, anddrawn by men distributed along the road at a distance of 100 metres : the waggon rollson planks, and the daily effect of each man is 900 to 1000 kilogrammes transported 1 kilo-metre : when there are inequalities in the floor of the gallery, which are otherwisesupposed horizontal, this effect is reduced to 600 kilogrammes transported to the samedistance.
Of Men acting on Pulleys. — According to Coulomb, ordinary rams used for driving pilesweigh 350 to 450 kilogrammes : a cord passing over a pulley sustains the ram on one side ; atthe other extremity of the cord different strings are attached, which men seize with theirhands : when the ram strikes the piles, the men hold the cord about the height of theirheads; bending at the same time as they apply an effort to the cord, they elevate the ramabout 1 1 decimetres. They make nearly 20 strokes in a minute, and three or four minutesin succession, after which they rest nearly as long as they have worked ; notwithstandingthis repose they are obliged to be relieved every hour. Men cannot perform more than threehours’ effective work in a day; the remainder of the time is occupied in placing and dis-placing the machines, dressing the piles, Sec. ; these works require slight effort, and affordtime for regaining the strength. In this experiment the number of men applied to themachine is such that each man lifts 19 kilogrammes of the ram.
According to these data the daily action has for its measure the product of these threenumbers, 11 decimetres, 19 kilogrammes, and the number of strokes given in threehours’ effective work, at the rate of 20 per minute, which gives 75 dynamic units.
Coulomb has followed, fifteen months in succession, the labour of coining money at Paris.These pieces are struck by means of a ram weighing 38 kilogrammes ; two men areemployed, and consequently each elevated a weight of 19 kilogrammes : the elevation was 4decimetres, and in one day 5200 pieces were struck, or, what is the same thing, the ramwas elevated 5200 times in a day, which gives for the daily labour 39i dynamic units. Inthe preceding example, we have for the measure of this action 75; but it must be remarkedthat the same men work in the Mint 15 hours in succession, instead of which, when drivingpiles, the men pass from one kind of labour to another when they are fatigued.
An Experiment made at the Bridge of the Militury School, under the Direction of M.Lamande, Chief Engineer of Bridges. — For driving piles a ram was used weighing 587kilogramme^ worked by 38 men ; at each blow they elevated the ram 1 -45 metre; after 30blows they rested a time equal to that of the blows. They gave 12 series of blows in anhour, or 12 strokes per minute, effective and continuous work : supposing they could havesustained this work 6 hours a day at 12 series of blows an hour, the daily labour of each587
man would be the product of or 15*44 kilogrammes multiplied by 1*45 metres, and by
72 series, 30 strokes, which gives 48 dynamic units.
Coulomb says, “ I have drawn water from a w*ell 37 metres deep : a man worked bymeans of a double bucket, attached to the extremity of a cord working over a pulley ; hedrew up the first day 125 buckets; the second 119, at 25 centimes per 10 buckets : themean effort, measured by a dynamometer, was 16 kilogrammes. We have the daily labourby multiplying the three numbers 16 kilogrammes, 37 metres, and 120, the number ofbuckets mounted in a day, the product is 71 great dynamic units.
Men acting on Winches . — According to Coulomb the pressure of a man in a continuouslabour exercised on the handle of a winch is about 7 kilogrammes ; most frequently theswiftness of the rotation of the handle is such, that each point describes in a minute 20 to22 circles, each of 23 decimetres. The duration of effective work in a day is about 6 hours :in this hypothesis the daily labour is the product of three numbers, 7 kilogrammes, 6 x 60minutes, 20 x 2 3 metres, or 116 great dynamic units.