ted, by practical men, seems to be, that these two processes, so essentially distinct, and which often actually counteract each other, are confounded, and frequently carried on in the same apartment. A furnace, to generate heat advantageously, should evidently be raised to a very high temperature, which can be effected only by surrounding it with non-conducting substances, and by giving to its exterior the color and smoothness least favorable to radiation. But these very circumstances, which fit a furnace for creating intense heat, entirely unfit it for distributing that heat to an apartment, or applying it to any external use. Hence might be inferred the necessity of having two parts to the apparatus;-one for generating or producing heat, and the other for using it. There are defects, also, in the prevailing mode of supplying air to the fuel to be consumed, in the form which is given to that fuel as a mass; in the practice of adding cold fuel frequently to the fire, by means of which its temperature is reduced, and its useful effect diminished;-on which we cannot enlarge in this place, but which have a material influence unfavorable alike to economy, convenience, and efficiency.*

CHAPTER VII

MACHINERY EMPLOYED IN THE ARTS.

In order to employ the mechanical agents, which have now been considered, it is generally convenient, and even necessary, to interpose between them and the work to be done some contrivance, called a tool or ma

*Since this paragraph was written, (1834,) the introduction of the hot blast into furnaces has created a new era in the history of industry. That, with other related improvements, was intended to be foreshadowed in the passage above, being, at that time, well known to the writer. A friend and relative of his, long known to the public, had proposed and introduced it, on a limited scale, some years before, and no doubt was entertained that it was destined to early and universal adoption.

chine. Before we proceed to examine the various arts, it will be important to attend, for a moment, to the construction and use of these machines.

The

Man does not excel the inferior animals more in intelligence than in bodily structure. If he has reason, which enables him to master every science, so has he a hand, which fits him for the practice of every art. bee and the beaver have intelligence, sufficient to guide them in rearing habitations and procuring food; and they have natural implements, which qualify them perfectly for the work. They need no tools, except the teeth and extremities with which Nature has provided them. Man, on the other hand, has an intelligence, which qualifies him for every office of duty or pleasure; and, instead of being fitted with natural implements, which could be employed only in one kind of work, he has the hand, fitted to fabricate and grasp every species of artificial tool, and equally ready for every occasion of peace and of war.

The powers of the human hand have been, in all ages, the subject of admiration. "By it," to use the language of Galen, (Book i., chapter 4,) "man erects the most various habitations, intrenches himself within camps or fenced cities, and weaves the garment that protects him from the Summer's heat or Winter's cold. With this, he forms the various nets and snares, which give him dominion, as well over the inhabitants of the water as of the air and earth; constructs the lyre and lute, and the numerous instruments employed in the several arts of life; erects altars and shrines to the immortal gods; and lastly, by means of the same instrument, he bequeaths to posterity, in writing, the intellectual treasures of his own divine imagination; and hence we, who are living at this day, are enabled to hold converse with Plato and Aristotle, and all the venerable sages of antiquity." of antiquity." Indeed, without this particular formation, man, with whatever sagacity he might be endowed, would no longer be the being he now is. "No bounteous grant of intellect, were it the pleasure of Heaven to make such grant," could raise him to his

present lofty rank, in the scale of power and enjoyment, if, instead of the hand, he had been formed with the claw of the tiger, or the talons of the eagle, or the hoofs of the elephant.

It is not without reason, then, that man has been defined, somewhat ludicrously, to be a tool-making animal. By nature, he is destitute of the tools which are necessary, in order to supply his wants; but finding himself endowed with a hand, admirably fitted to make and wield these tools, he tasks his ingenuity, and soon produces them. How wonderfully does even the rudest cutting instrument enlarge the powers of the human hand! the fabrication of many things, which were previously beyond its means, becomes easy, and that of others possible, with great labor. Add the saw to the knife or the hatchet, and other works become possible, and a new course of difficult operations is brought into view and thus does man perpetually advance 'in power and resources, till at last he provides himself machines, of the utmost complexity and perfection; machines, which supersede even the hand itself, and perform the most delicate and difficult operations, with all the precision and regularity of an intelligent being.

All machines, however complicated, are formed by combining a few simpler machines, commonly called the mechanical powers. Under this head are usually enumerated the lever, the wheel and axle, the inclined plane, the screw, the wedge, the pulley and rope. Of the lever, we have examples in the common crowbar and handspike; in the pump-handle; in the hammer, when used in drawing a nail; in a door opened by the hand; in steelyards, scissors, &c.* Of the wheel and axle, we have examples, in the windlass used for raising heavy weights, where the power is applied to the circumference of the wheel, and the weight, or resist

* Levers are of three kinds. Fig. 18, is a lever of the first kind, resting on the fulcrum, at F, to raise the weight, W, the power being applied at P. Fig. 19, is a lever of the second kind; W, the weight, being between the fulcrum, F, and the power, at P. Fig. 20, is a lever

ance, to the axle; also, in the capstan used on shipboard; in the crane; and in the grindstone, where the instrument, pressed on the stone, forms the weight or resistance, the power being applied to a crank, which corresponds to the wheel. It is obvious, that this wheel and axle is, in principle, merely a lever, with the addition of a rotary motion around the fulcrum, or axis.*

of the third kind; the power, P, being applied between F, the fuland W, the weight.

crum,

Of the inclined plane, Fig. 23, we have an example in the plank, which is used in letting down heavy casks into a cellar, or drawing them

Fig. 23.

Fig. 24.

up; and the screw is in principle the same; being an inclined plane of the spiral form, like the stairs which we sometimes see in the inside or outside of a building, winding to the summit. In some cases, the spiral or screw is fixed, and the power is applied to a nut, as in Fig. 24. In other cases, the nut is fixed, and the screw, with

the weight attached, is moved through it by being turned, as in Fig. 25. The wedge, Fig. 26, is another spe

cies of inclined plane, being formed, in most cases, of two inclined planes united at their bases. In addition to the common wedge, we have, as examples of this machine, various cutting tools, such as axes, knives, chisels, &c.; the nails and spikes to be driven into wood; the coulter of the plough, and the blade of a spade, &c.

The pulley and rope are sufficiently familiar, without other examples than in the annexed figures, (27, 28, 29,)

Fig. 27.

Fig. 28.

Fig. 29.