Chap. XV.
ON MECHANICAL AGENTS.
1091
Of a Man pushing as he watts, or drawing harnessed. Mill-walk in the Wells of Bicetre -
The Bicetre contains three establishments: the hospital for the mad people, the prison, andthe infirmary. Those who are least diseased, mostly the epilectic patients, receive a smallremuneration for drawing water from a well; 72men are designed for this service; 24 onlywork at once, for 1 hour 20 minutes in succession, and are replaced by others for the sametime.
The mill-walk is in an octagon tower, whose opposite faces are 11 *69 metres distant; thecentres of the horizontal bars which the men push before them while walking are on acircle 5-2 metres radius ; these bars are directed towards the axis of the mil); 16 men walkwithout the walk and 8 within ; there arc 8 couples of men, and each couple push the samebar; the distance between two men of the same couple is 8 decimetres ; the height of thebars above the ground is 9 decimetres ; the distance between two consecutive bars is1 *3 metres ; each man is placed between two bars, which he pushes alternately before him,according as the wheel is to turn in one direction or the other.
The well is 52 metres deep from the surface of the water to the crochet which emptiesthe buckets; the interior diameter is 4-872 metres; the water constantly stands at 4*872metres from the bottom.
A vast reservoir of a square form, well vaulted, contains more than 1000 cube metres ofwater ; the vault is supported by 16 columns, which serve as piers to 9 elliptical arches :this reservoir, the tower, and the well, were executed in 1733-4, from the designs ofBoffrand, engineer of bridges and roads.
Of the Swiftness of Men pushing the Bars of the Mitt. —The men make 8.J turns in5 minutes, the time necessary to elevate a bucket from the surface of the water to the bank,taking the mean walk of 24 men as a circle of 10‘4metres diameter ; the 8£ turns correspondto 278 metres, which gives 0-92 metre for the velocity in \ n .
Useful Effect of the moving Power. — In a relay of 1 h. 20 / , or 16 times 5', they raise 16buckets ; a bucket contains 700 litres, weighing 700 kilogrammes : thus the useful effectof 24 men is 700 kilogrammes x 16 x the height to which the water is elevated, or 52metres, and for each man this number divided by 24, that is to say, 25 great dynamicunits of a cube metre of water elevated 1 metre. The remuneration of this work is 8 cen-times a man.
The waters of Arcueil , and other sources more elevated than the Bicetre, bring togethersix months in the year a considerable quantity of water, and then four or six relays sufficeto draw from the well the water necessary for the service of the establishment; but insummer the natural sources fail, and each labourer makes four relays, which causes hisdaily labour to be 100 dynamic units; it is only one-half during six months of the year, sothat the mean daily labour is 75. The quantity of water drawn in 12 relays is expressedby the product of the three numbers 700 litres x 16 x 12, or 134400 litres. The popu-lation of the Bicetre being about 3000, we have nearly 45 litres for each individual;it is generally supposed that 20 litres for each person would suffice for the wants of a greattown ; on account of the baths watering the gardens of the Bicetre, the consumption ismore than double.
The Force developed by the Mover. —It was intended to measure, by means of a spring, themean pressure of men on the bars of the mill at the Bicetre; but this project was abandonedon account of the great inequality of force in the individuals, more or less weakened by ageand infirmity. The resistance to be overcome is unequal, but it is at its maximum whenthe buckets rise from the water, whilst the other begins to descend ; the cables carryingthe buckets are 2 decimetres in circumference; each passes over a pulley T3 metres indiameter, and coils round the drum of the machine, whose diameter is 1*9 metres; the partof the cable comprised between the pulley and the level of the water in the well weighs250 kilogrammes. The resistance which acts tangentially to the drum will be 700kilogrammes, the weight of a full pail of water added to the weight of the cablewhen the bucket begins to ascend, and subtracted from that of the cable when thebucket is at the height of the hook, which is inclined to empty it; thus the resistancevaries from 850 to 550 kilogrammes. The buckets weigh, when full, iron and woodcomprised, 600 kilogrammes, but one always equalises the other, and we must only countit as inertia: the distance of the axle of the machine to the vertical axis of the well isabout 13 metres: whatever is the weight of the cable, the mean resistance being 700kilogrammes, acting on a radius of 3 feet, the power producing the equilibrium will be atthe extremity of the radius 1 6h feet; taking of 700 kilogrammes, gives 127 kilogrammesfor the total pressure on the bars. If we subtract the inertia and friction of the cable onthe pulleys and on the drum, the mean pressure of 24 men working the machine will be127
2^- kilogrammes, or 5 metres 3 kilogs. On account of the inertia, friction of the ropes
on the pulleys and drum, we suppose the mean pressure to be 7 kilogrammes, so that therelation of the useful erfect of the force developed to produce it is that of 5*3 to 7, or 0*8to I; that is to say, a fifth only of the force developed will be employed to overcome friction
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