into lengths by descending blades. These blades are three in number-two lateral, at right angles to the rod, each of which cut straight through the centre of a prominence, so as to divide it into two nail heads; one central, set obliquely to the rod, so as to divide each interval into two bevelled points. The pieces, now called nail blanks, are next put into a machine like a huge coffee-roaster, which is kept turning in order that they may clean and polish each other by mutual friction.

The cleaned nail blanks still require to receive their perfect shape, and for this purpose they pass through two machines, the first of which gives a generally pyramidal figure to the heads, while the second finishes the shape in all respects. The first, or heading machine, consists of a massive die, which rises and descends in a vertical line. Beneath it a wheel turns intermittently on a horizontal axis, and from the circumference of this wheel project several pairs of dies, which receive the nail blanks point downwards. When the vertical die descends it finds one of the pairs of wheel dies beneath it to receive the stroke; and each stroke of the vertical die is followed by a partial revolution of the wheel, which brings the next pair of wheel dies to receive the next blow. The wheel dies consist of blocks of iron hollowed out on their opposing faces to receive the blanks, and hollowed at the top into the proper shape of the heads. The two blocks are kept somewhat apart by spiral springs inserted between them, so that they hold the nail blank loosely; but as each pair in succession reaches a vertical position, and just before the plunger descends, a pair of grippers closes upon the blocks and squeezes them tightly together, so that the blank is held securely to receive the blow. As the plunger rises, the grip is relaxed, and the blocks are again separated by the springs. As the wheel passes on, each pair of blocks receives, in its turn, a tap from a mechanical hammer, by which the nail blank is loosened, so that it falls out as soon as its head is directed downwards by the continued revolution of the wheel. The machine is supplied by one girl, who sits

by the revolving wheel, and places nail blanks in the wheel dies as they successively ascend towards her. A single machine is capable of heading from 22,000 to 24,000 nail blanks in a day of ten hours.

The shaping machine bears a great general resemblance to the foregoing. The nails are carried up, one by one, on the circumference of a wheel, on which they are retained by stops, and are presented in succession to the pressure of a descending plunger and of two lateral dies, which between them remove all irregularities or inequalities of form, and produce a nail of perfect finish and outline. Lastly, the nails are annealed and coloured, and are then ready for the market.

With the exception of the men employed at the rolling mill and the annealing furnaces, the work of the factory is mainly done by girls, most of whom were employed, until recent changes, in Woolwich Arsenal. Besides the saving thus effected in the cost of labour, there will also be an important saving in material. In hand-made nails the waste of iron is not only very considerable, but is absolute, and cannot be recovered. In Mr. Huggett's process there is a primary waste of about 24 per cent. of raw material; but 19 per cent. of this is in the shape of odd lengths of metal, defective nails and so forth, all of which can be again worked up and rendered useful. The irrecoverable, or fire waste, does not exceed the remaining 5 per cent. By means of these elements of saving, Messrs. Moser expect to be able to sell at about 10 per cent. less than the cost of the cheapest hand-made nails, and as none but the very finest iron would lend itself to their rolling process, the quality of the metal is uniformly of the best. The machine-made nails may be bent two and fro upon themselves without breakage, twisted in every conceivable way, or beaten out into sheets as thin as writing-paper without cracking at their edges. The whole process is a triumph of mechanical ingenuity, the more curious and interesting that it has been so long delayed.-The Times.

THE ATMOSPHERE AND ITS MOVEMENTS.

AROUND the earth, over sea and land, extends a vast expanse of gaseous matter; it is known as the atmosphere, through whose instrumentality all life exists. The atmosphere, (or as we generally call it the air,) consists of a compound of gases, the two chief being oxygen and nitrogen, which are mixed together in the proportion of seventy-nine of the latter to twenty-one of the former. Many substances pass into our air in a gaseous state, and make their presence felt, so that we can very seldom obtain thoroughly pure air. Flowers diffuse their odours through it: the breath expelled from the human body poisons it.

The atmosphere performs most important offices; and since it is everywhere existent it is all-important. The tree or flower yields up its oxygen to the air, which transfers it to man, thereby strengthening and reinvigorating him. Man expels from his frame carbonic acid, which the air carries to the plant, thereby refreshing it, so that man and plant perform mutual offices the one for the other.

The atmosphere extends above the earth for a distance of forty-five miles. It is very elastic, hence the densest part will be at the sea-level, where the weight of a column of air of the atmosphere's entire height has to be sustained. The pressure at the sea-level is at the rate of fifteen pounds to the square inch. We are not conscious of this pressure, because natural laws prevent our feeling it. "The little limpet, however, feels it, and makes use of it too, when he sticks so hard to the rock, that you cannot pull him off. By a peculiar faculty he removes the air and water from between him and the rock, and it is then simply by atmospheric pressure that he clings so tightly."

Any considerable change in the lightness or heavi ness of the air, would be fatal to animals. Those who climb very high mountains, and thus reach the higher

and thinner parts of the air, find a greater difficulty in breathing, are unable to exert themselves, to lift weights, or even to stoop, and sometimes are compelled to come down, from the danger of breaking some bloodvessel, in consequence of the outward pressure of the air being taken off. On the other hand, those who go down in diving-bells, and have the air which they breathe, pressed into a narrow space by the water above them, find inconvenience from that cause.

I. One most useful property of the air is to convey sounds, not only in a rude way, by making us hear loud noises or low murmurs, but by exactly representing those most delicate inflections of voice, which constitute speech. It can be proved by direct experiment made by the air-pump-a machine by which the air can be drawn out of a large glass receiver-that if a bell be hung in such a glass, and the air be pumped out, there is no sound whatever produced, although the clapper be struck against the bell. Sound is, in fact, a vibration something like waves, carried along from one part of the air to another. It does not move so fast as light, as anyone may perceive, who observes a gun fired from a considerable distance. He will see the flash some time before

he hears the report, just as we hear the roar of thunder some seconds after we see the lightning.

The air, then, which we breathe, is exactly fit for conveying such sounds as our voices are able to produce, and our ears are fitted to hear. But it is not every kind of air which will do this. If a man's lungs are filled by breathing some gases, which can be produced by chemical means, the sounds which his voice is able to make can scarcely be heard. And no doubt this difference would be much more perceptible, if the ears were also surrounded by such an elastic fluid, instead of common air.

Without the air, we should be in a state of utter silence; and if it differed much from what it is, we should never have conversed. All language, all communication of thought by speech, could never have existed. And without speech, what would have been the condition of mankind?

II. The air has also very material influence upon our sense of sight. It is by the action of the atmosphere only, that the change from day to night comes on so gradually, indeed so imperceptibly, that the eyes easily accommodate themselves to it. Had we little or no atmosphere, the rising of the sun would cause a sudden change from utter darkness to the light of the brightest noon and at his setting, we should again be instantly left in darkness. It is almost needless to

observe with how much beauty this beneficial change is now accompanied. All the glowing colours which decorate the heavens, at the rising and the setting sun, the thousand brilliant hues in which the clouds are bathed, are all owing to the atmosphere.

Colours are given to various objects by their absorption or reflection of certain rays. A red object is red, because it absorbs into itself the rest of the primary colours, and reflects the red. Another object is violet, because it reflects only the violet rays. A black object is black because it absorbs all the colours, while a white object reflects all the colours. You can see the seven primary colours in the rainbow. You can easily see how the union of the colours makes white, by painting a top with the seven colours and then spinning it; as the top goes round, the colours will appear to blend together, and the top will look as if it were painted of a dustywhite colour.

III. Again, the atmosphere is the agent by whose means we receive light and heat. Both consist in the communication of motion from the sun; certain vibrations produce light, while others produce heat: but all bodies do not allow heat and light rays to pass through them. Had the earth been surrounded by glass instead of air, we should have received all the light that proceeds from the sun, but none of the heat. Air is both transparent like glass, and a conductor of heat like rock-salt.

It is by means of the atmosphere that we are able to see objects in the day-time, in whatever part of the sky the sun may be. No object can be seen