1088
THEORY AND PRACTICE OF ENGINEERING.
Hook II.
Sometimes the duration of effective work is confounded with the time which a man passesat the shop or the machine which he moves; nevertheless these two periods of time are verydifferent; if a man walks and makes a halt of some minutes, we must regard the duration ofthe halts as a part of the time of rest, and must be added to the time of sleep and food. Itis the same with all other work which requires an alternation of action and rest, only con-sidering that the duration of action diminishes at the same time as the moving power or theintensity of the momentary effort of the mover augments. It has been observed that a manor horse developes the power of which he is capable, in a day of 24 hours in a very variabletime, which is at least one hour, sometimes 1^ hours and generally 8 to 12 hours.
When we can regulate the two elements of daily labour, the moving power and the timeof effective labour, it would be desirous that we should find the value of those elementswhich determine the greatest effect of daily labour: by multiplying the experiments on agreat number of men, and for several years in succession, we shall ascertain exactly thevarious daily labours or at least the limits of these actions, having a regard at the sametime to the natural strength of the individual, to climate, and all the circumstances whichmodify this force.
On the Velocity with which Man moves.-— This depends on various circumstances, forwhen walking on a plain without a load, he moves at the rate of 13 or 16 decimetres persecond: according to the observations made by Bouvard during a review of the troops atthe Champ de Mars at Paris , 251^ metres were passed over in 33 seconds, which is atthe rate of 7 *7 metres per second. Soldiers when marching at ordinary time take 76 pacesper second, and pass over 50 metres: when this pace is accelerated 100 paces in the sametime, and they pass over 66 metres: when marching quick, 230 paces are made per second,and 130 metres are passed over. This gives for the ordinary and accelerated time 0'66
50
metres, or 2 metres for 3 paces ; and in 1 second of time ^ of a metre at ordinary time,
^ when accelerated, and when at quick time. When a man is travelling without a
load, and on level ground, he performs from 40 to 50 kilometres per day during the 8or 10 hours he is engaged out of the 24. The French soldier carries a load equal to 18j 7 0kilogrammes in time of peace, and 25\ in time of war.
Daily Labour of a Man has for its measure the resistance expressed in weight, multipliedby the road ; and when he walks over a level road, the resistance he overcomes at eachinstant is unknown : when he mounts a staircase, at each step he elevates the weight ofhis body ; the height of the riser and his weight we consider as the measure of resistance ;so that the daily labour has for its measure the product of the weight of the body,multiplied by the height to which it is elevated during the effective labour of one day.
According to an experiment made at the Peak of Teneriffe, which is 3780 metres abovethe level of the sea, 8 men loaded with 7 or 8 kilogrammes, who accompanied Borda, wereelevated the first day 7£ hours’ effective work, to the height of 2923 metres. Supposing theresistance equal to the weight of a man, which is 70 kilogrammes, augmented by a load of7 kilogrammes, we have for the measurement of the action in a day of each of the 8 men225 cube metres of water elevated 1 metre; the ramp being 20 kilometres, the fall willbe 14 centimetres per metre. The man who mounts with two motions, one horizontal, andthe other vertical, each of which has a separate resistance, the sum of them must be taken,which we suppose equal to 77 kilogrammes. In this experiment the height to which aman is elevated in a day is not that to which he elevates himself by walking moderately,for Coulomb offered to labourers the price of a day’s ordinary work to mount IS timeswithout burden on a ramp of 150 metres height, or, what is the same thing, once to aheight of 2700, and they constantly refused.
It is, therefore, probable that a man travelling in a mountainous country without a load,and at a gentle elevation, would terminate his journey when he was elevated 2 kilometres,after marching 8 hours, whilst he could at the same time, and without fatiguing himself,move 40 or 50 kilometres on a level road : by only counting on a march the effortnecessary to elevate at each pace the entire body above the surface of the earth, and sup-posing this elevation to be 3 centimetres, the total elevation will be the number of stej smultiplied by 3 centimetres; or, the number of paces is the quotient of the number ofmetres gone over in a day, multiplied by the length of the steps, or 400C0 metres divided by0*66, which is 66666; multiply this by 0*3; the product is nearly 2000 metres, equalto the height of the ramp. The act of walking consists in gliding over the earth,and elevating the centre of gravity as little as possible; this first effect produced, he mustalso give a horizontal velocity ; this second effort of walking requires an effort which isadded to that which precedes for the elevation of the body, but which is evidently muchless. We know no experiment which determines the relation of these two efforts. Mul-tiplying 2 kilometres by the weight of the man, 70 kilogrammes, we have for the measure-ment of his daily labour during the length of his march in mountainous countries 140units, each unit being a cube metre of water elevated 1 metre.