Chap. XV.

ON MECHANICAL AGENTS.

1089

If a man mounts when loaded, this action will diminish, as we shall see by the followingexperiment of Coulomb’s : he observed that a man may carry in a day six loads of woodto a height of 12 metres, each being 734 kilogrammes, carried in 11 journeys, or the6 loads in 6.^ hours. Thus the man made 66 journeys, and elevated a weight of 6 x 734kilogrammes of wood to a height of 12 metres, or 53 cube metres of water to a heightof 1 metre. He elevated himself 66 times to a height of 12 metres, and this work isexpressed by the number 56, the product of three numbers, 70 kilogrammes, 12 metres,and 66 journeys. Adding this number to the preceding, we have for the measurementof the daily labour of a man who mounts loaded, the number 109, less than the 140 foundbefore.

In the experiment made on the wood porter, each burden of ^ 4 , or 67 kilogrammes, weremounted in 1-j'g minute, so that the duration of the principal work in a day of 24 hours was1 hour 12 minutes ; this work was paid at the rate of 1 franc per load of wood mounted 12metres. Hie time which elapsed between the two consecutive mountings was aboutbreathing time ; it was employed in loading the crochets, log by log, in descending thestairs, &c. ; it appears that this method of dividing into short intervals of work and restthe labour of men carrying great burdens, is that which agrees best with the animaleconomy, and that men prefer a very fatiguing action of some moments, followed by thetime necessary for rest, to a less powerful exercise, but more continuous and of longerduration.

The result of the experiment cited by Coulomb differs very little from that which Gue-niveau relates in his Essay on Machines; this engineer observed the workmen whomounted from coal mines by very steep and inconvenient stairs; their load varied from35 to 40 kilogrammes, and the daily elfect was 42 to 50 kilogrammes elevated 1 kilometre :taking the weight of the man into consideration, 70 kilogrammes, the daily labour wouldVary from 112 to 120 dynamic units.

Loads of equal weight fatigue much less in proportion as they arc distributed equallyon all parts of the body ; a man carrying a weight equal to his own, and mounting a ladderof a given length, would fatigue himself more than if he mounted without a load by thesame ladder to double the height: although in these two cases he would produce thesame dynamic effect, the second height would produce much greater fatigue than the first.

Coulomb often proposed to different porters to carry furniture from one house toanother at a distance of 2 kilometres on a horizontal road, loading themselves at each journeywith a weight of 58 kilogrammes ; they all told him that they could only make 6 journeysper day, at 1 franc 50 cents per journey ; they added that they could not sustain a similarfatigue two days in succession.

Several hawkers were interrogated as to what was the greatest weight they could carryin their journeys, and how far they could go with this weight; the strongest of themanswered that, loaded with 44 kilometres, they could not proceed farther than 18 to 20kilometres in a day.

We conclude from these different experiments that the action of walking with or withouta load on a plain, or in a mountainous country, is bounded by limits which depend on thedevelopment of the vital forces, which are very variable, and have no absolute measure.

The resistance surmounted at each instant by an animated mover is only to be determinedand measured when this resistance is without the mover : in this case the mover exerciseson a point which resists a pressure equivalent to that of a weight. The man who walkseither with or without a load exercises two kinds of pressure, one on the ground, theother on himself; the latter is not known; whence it follows that there is no absolutemeasure of the daily labour of a man walking, and it differs essentially from those laboursin which we only consider the pressure exercised on an exterior object: of whatsoever kindthese labours may be, they are only to be compared to those when they produce the samedegree of fatigue, and when animated movers can sustain the daily labour which is an ob-ject of comparison, without injuring their physical constitution.

Of the daily Labour of a Man moving a Load on a JFkeelbarrow , or other small Carriage -

Pascal was, it is said, the inventor of the wheelbarrow : this machine is a case longerthan it is wide, attached to a frame, whose arms are longer on one side than on theother. The shortest side carries the gudgeons of the axle of a small wheel. The loadis placed in the case, and the man charged with transporting it seizes the handles of thebarrow at about 15 decimetres from the spindle. The total weight of the barrow is about30 kilogrammes, and it is loaded with 70 kilogrammes when used for moving earth. Vauban ,whose name recals the epoch of the greatest earthworks, observed that a man in his dailylabour can make 500 journeys of 29 metres each, with a barrow loaded with 70 kilogrammes :to compare this effect with that which we obtain from porters loaded with crochets, we shallestimate the daily labour of the latter by the weight transported, and the distance passedover. Thus, we have for the effect of the hawkers in a day 44 kilogrammes x 20 kilometres,and for that of the workmen with a barrow 70 kilogrammes x 14*5 kilometres. Thesetwo effects arc in the relation of 880 to 1015; thus, if we only regard the weight of the

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