MANUFACTURES.

13

\Unu- time during which the brine falls through the fagots, holds in solution as much moisturet " re ^l as it can contain in an invisible state, none can be absorbed from the salt water, andthe labour expended in pumping is entirely wasted. The state of the air, as to dryness,is therefore an important consideration in fixing the time at which this operation is tobe performed; and an attentive examination of its state, by means of the Hygrometer ,might be productive of some economy of labour.

VII. exerting forces too large for human power.

It requires some skill and a considerable apparatus to enable many men to exerttheir whole force at a given point, and when this number amounts to hundreds or tothousands additional difficulties present themselves. If ten thousand men were hiredto act simultaneously, it would be exceedingly difficult to discover whether each exertedhis whole force, and consequently, to be assured that each man exerted the force forwhich he was paid. And if still larger bodies of men or animals were necessary, notonly would the difficulty of directing them become greater, but the expense wouldincrease from the necessity of transporting food for their subsistence.

In all our larger Manufactories numerous instances occur of the application of thepower of steam to overcome resistances which it would require far greater expense tosurmount by means of animal labour. The twisting of the largest cables, the rolling,hammering and cutting large masses of iron, the draining of mines, all require enor-mous exertions of physical force continued for considerable periods of time. Othermeans are had recourse to when the force required is great, and the space through whichit is to act is small. The Hydraulic Press of Bramah can, by the exertion of one man, H ^ s raulicproduce a pressure of 1500 atmospheres, and with such an instrument a cylinder ofwrought iron three inches thick has been burst. In rivetting together the iron plates Rattingout of which-steam engine boilers are made, it is necessary to produce as close a jointas possible. This is accomplished by using the rivets red-hot; and while they are inthat state the two plates of iron are rivetted together, and the contraction which therivet undergoes in cooling draws them together with a force which is limited only bythe tenacity of the iron of which the rivet itself is made.

VIII. EXECUTING OPERATIONS TOO DELICATE FOR HUMAN TOUCH.

It is not alone in the greater operations of the Engineer or the Manufacturer, thatthose vast powers which Man has called into action, in availing himself of the agencyof steam, are fully developed. Wherever the individual operation, demanding little forcefor its own performance, is to be multiplied in almost endless repetition, commensuratepower is required. It is the same “ giant arm which twists the largest cable,” thatspins from the cotton plant an “ almost gossamer thread.” Obedient to the hand whichcalled into action its resistless powers, it contends with the ocean and the storm, andrides triumphant through dangers and difficulties unattempted by the older modes of

Sect. I.