leaving the starch unchanged in its qualities.

Now, three solvents have been proposed, at different times, for this purpose. The first was sulphuric ether; which, though it does effect solution, yet, as it must be pure, and as it is exceedingly expensive, is out of the question for common purposes. The second solvent pro-posed, was oil of turpentine; which, however, being found difficult to dry, was abandoned. The third was rectified coal-oil, or naphtha, as it is called. This oil is a more powerful solvent than the former, and it dries more readily, but still so imperfectly as to leave the caoutchouc clammy, and too devoid of firmness to bear any of the fatigues of wear.

Such was the progress that had been made previous to the invention which is the more immediate subject of this notice.

Mr. Macintosh's process is exceedingly simple. The caoutchouc is put between two plies of cloth, which it cements so completely, that, when the cloth is not thick, and both plies the same, it would readily be taken for a single ply. For this purpose, two appropriate pieces of cloth are selected, one for the outside, and the other for the lining. These are stretched on tables, or frames, by the common means employed in calico-printing processes. A thin coating of a solution of caoutchouc, in naphtha, is put on each of them, and is allowed to dry. A second is then put on each and also allowed to dry, and likewise, if necessary, a third, and a fourth. At last, a coating is put on one of the plies, and the other ply (with varnished side to varnished side) is put above it, and spread upon it evenly. It is then dried in a stove, to remove the smell of the oil. Lastly, it is smoothed by being passed through a calender.

This process greatly strengthens the cloth, without materially altering its appearance. The different plies of cloth may be either of the same kind, or different; woollen cloth to woollen cloth; cotton cloth to cotton cloth; silk to silk; woollen cloth to cotton cloth; or, cotton cloth to silk, &c. Woollen cloth, with either a silk or a calico lining, makes an excellent cloak. But of the specimens which we have seen, we admire most those of which both plies are calico. This, we think, makes a light, and an elegant cloak, perfectly waterproof. Indeed, we conceive that the great improvement which this process of waterproofing has introduced, consists in affording complete protection from the inclemencies of the weather, and of situation, by means of a light fabric, what has hitherto been afforded, only imperfectly, by means of heavy fabrics.

No one, who has ever been at sea, can doubt its usefulness in the dress of sailors, by which they can be supplied with trowsers and coats through which not a drop of moisture can penetrate, and on which the sea may break, and the rain pour in vain.

The same process likewise renders the fabrics air-proof. Among the numerous uses to which this property of the fabrics will introduce the process, we may mention bags for holding air, in the form of loose shirts, which, on the emergency of a shipwreck, may both enable the sailor to reach the shore, and protect him from being bruised against rocks.

Portable military beds, filled with air, were proposed a few years ago; and a late eminent town'sman of our own was of opinion, that beds filled with air would suit for general use. Mr. Macintosh's process appears to us excellently calculated for this purpose. Not that the Glasgow Mechanics' Ma

gazine would encourage him that “foldeth the hands;" no such thing. An air bed would, by no means, be so soft as a feather bed; it would partake rather of the hardness of the mattress, with this difference, that firmness, rather than hardness, would be its characteristic. Such beds should have sides all around, in the common form of the mattress, and, like them, should be bound together internally. From the nature of the varnish employed, we are convinced that no vermin would approach such beds; a circumstance which, however vulgar the mention of it may be esteemed, is a great recommendation to the plan, for hot climates, for ships, and for general use. Air beds, we seriously think, would be found more comfortable than either feather beds or mattresses; and the improvement would be very great, if (being perhaps equally economical) they would supersede the use of those containing chaff, straw, heather, and the like.

In looking at the probable utility of Mr. Macintosh's invention, in this and many other respects, we think that the state of any army employed in the field may undergo a very material improvement, as to the improvement and health of the troops, provided it were rendered available in this department.

Shoes made waterproof by this process, may literally be said never to be wet; as no water, however much they may be exposed, can ever penetrate farther than the surface.

In the construction of all architectural works under water, such as bridges, piers, docks, &c. there cannot be a doubt that the waterproofed cloth will be almost immediately adopted, instead of the copper, at present employed; being far more manageable, and a better defence against the water.

Before leaving the subject, we

think it proper to point out some uses of this invention less apparent than some of the preceding.

Paper may also, by the same process, be made equally waterproof with cloth, leather, &c.; and in this way it will be very much changed in its nature and characters, while its appearance remains nearly the same as before.

Dr. M'Culloch has pointed out, in a series of experiments recently published, that a mixture of any of the essential oils prevents paste, or batter, from moulding, and suggests many advantages resulting from such a discovery where paste is used. For example: in bookbinding, and in cabinets of natural history, in the waterproofing varnish, the naphtha employed will undoubtedly possess the same property, with this important additional advantage, that no moisture, which is the cause of moulding in books bound in leather or paper, can ever penetrate the surface of waterproofed leather or paper. In this branch, the advantages of the invention may be of scarcely calculable extent: as it will secure in a state of perfect preservation, for ages, books which, in the present state of the art, might be expected, in a short time, to fall a prey to the effects of damp, or to be devoured by the worm or moth.

The only method by which our finest works stand any chance of resisting at present the last mentioned enemy, is, by being bound in Russia leather, the peculiar odour of which seems to be insupportable to them; and the mode of preparing which, is, or was, till very lately, unknown in this country. Now, the slight degree of smell which waterproofed leather acquires in the process, and which is not more disagreeable than that of Russia leather, will, in all probability, render it an unpalatable food for the moth; and the caout

chouc employed in the preparation of the varnish, will entirely alter leather and paper, as a digestible food for the destructive insects in question. The linings of carriages, and furniture of cloth and silk, although not exposed to the action of the weather, still, after a short time, moulder into rags, from the ravages of the Tinea, or clothes moth. This process, there can be little doubt, as communicating to them a new property and character, will secure them from the tooth of this insect; so that even where an immediate necessity for the use of waterproofed substance does not appear, an extensive field of usefulness may be opened for the application of the invention.

Drawings or writings made on waterproofed paper, or enclosed in a portfolio made of it, may continue under water, for any length of time, uninjured. Its use, in room of parchment, or the common paper employed for legal purposes, must, for the reasons already stated, be obvious, as it possesses powers of durability far superior to either; and silk, prepared in the same manner,

affords a surface much better calculated for writing upon than parchment: and, from no lime being necessary to prevent the ink from running, as is the case with parchment, the ink will retain its colour to the last; whilst that used upon vellum and parchment, it is well known, can, with difficulty, be prevented from decaying.

In concluding this notice, we find that we have made it much more of a discursive nature than we at first intended. In referring to the process, we have found ourselves under considerable embarrassment; as, though we have every reason to be grateful for the liberal communications which have been made to us, yet, owing to the absence of the patentee, we are prevented, for the present, from procuring the specification. On a future occasion, we shall present this document to our readers, accompanied, if necessary, with farther observations.

After the details which we have given, we need scarcely say, that we consider the invention simple, ingenious, economical, useful; and, as such, creditable to the inventor.

OF

on mind, and, leaving those subtle and idle fancies, that so long deluded the learned world, to the metaphysician or moral philosopher, confines himself entirely to the study of matter, and its laws.

On the Properties of Bodies.

Metaphysicians have given very different definitions of matter. Some have even doubted whether we can have a moral certainty of our existence. The natural philosopher does not enter into these discussions. Resting uniformly upon experience,

he denominates all those bodies material which produce a certain assemblage of determinate sensations upon our organs; and the power of exciting in us these different sensations, constitutes for him so many properties by which he may recognize the presence of bodies. But, among these properties, two only are essentially necessary to produce in us the sensation of matter; these are extension and impenetrability, of which the sight and the touch are the first judges.

Extension.

The characteristic drawn from extension is self-evident. When we see, or when we touch a body, this body, or if you will, the power of acting upon our senses which it possesses, resides in certain parts of space and not in others. The place where it resides, is, therefore, determined, and in this even its extension consists.*

Impenetrability.

When we follow the outline or boundary of a body by the touch, we perceive that the matter of which it is composed is external to ourselves. In general, two distinct portions of matter can never be identified with one another, in such a way, that the same physical points of space can give us at once the

*The extension of a body in every

direction determines the figure of that body; and it may be said, that the figures of bodies admit of an infinite variety. Many, however, present regular and determinate figures, which indicate the action of causes operating according to certain fixed laws. These bodies are called crystals, and have a strong analogy to the regular solids contemplated by geometers; which forms they generally take, with various modifications. Extension and figure being the subject of geometry, the student of mechanical philosophy ought to make himself acquainted with the former science, if he is desirous of making any very considerable progress in the latter.

sensation of both. It is in this that its impenetrability consists.

To explain how the union of this property with extension is necessary to the existence of a body, we shall take an example where these properties can be observed separately.

When we place a small object before a concave mirror of polished metal, of which the surface is spherical, it forms, at some distance from the mirror, an image, so much resembling the object, that we can see it very distinctly, if we place it at a proper distance. This image, distinct from the parts of space which immediately surround it, is extended, but not impenetrable. You can plunge your hand into it, without experiencing the least resistance, and the parts which you touch are not displaced, but vanish in proportion. Assuredly, you could not thus penetrate a piece of wood or stone, or any other of those bodies which are called solid. You could even, if you place another mirror in a proper position, cause the image of another object to coincide in the place of this same image, without displacing, or even in any way deranging it.

You could produce the same coincidence with the image of a third object, of a fourth, and as many as you please. All these images are extended, but not impenetrable. They are the forms, but not the palpable matter; this term is necessary, for we shall see afterwards, that the light which determines those images is, itself, composed of small material particles of an insensible tenuity, which move with an extreme swiftness, and do not dissolve here, but pass through among one another in the spaces by which they are separated.

Here it becomes necessary to notice some very simple phenomena, which seems, at first sight, to contradict the impenetrability of matter, but which, on the contrary,

when examined more minutely, do not fail to confirm it.

When we let fall a solid body, for example, a mass of gold, into a fluid, such as water, it sinks in it, and seems to penetrate it; but it has, in reality, only caused the separation and displacement of the parts; for, if the vessel which contains the water terminates at the top in a narrow neck, we see the level rise in the neck, in proportion as we increase the volume of the body immersed. There is, in this

case, therefore, a division and a separation, but not an intimate penetration of the parts. The same thing takes place when we drive a nail into a plank, or when we cleave wood with an axe; only the parts of these bodies admit of separation with more difficulty than those of water. The same thing occurs, also, if we drive the nail into a mass of clay, of lead, or of gold, in either of which it only makes its absolute place. Indeed, the mass

thus

pierced, is not entirely disunited, but its parts are merely pressed and driven back upon one another; and if we take out those parts which surround the hole which the nail has made, we shall find in them sensible traces of this pressure. The nail, in its turn, can be thus pierced by steel, and this, again, can be punctured by other bodies.

This teaches us, that even the hardest and most solid bodies are not composed of matter absolutely continued, but of parts collected together, and placed at distances, which may become greater or less, under the influences of exterior causes. This explains how the same mass of matter increases in bulk, by the effect of heat, and contracts by that of cold; how the particles of salts, spread during their separation, and are lost, so to speak, among the particles of water; how mercury attaches itself to the

The impenetrability of bodies may be farther illustrated and confirmed by the following simple experiments:

1. A vessel being filled to the brim with water, if any solid, incapable of dissolving in that liquid, be plunged into it, a quantity of the water will overflow, equal to the bulk of the solid immersed.

2. If a cork be thrust hard into the neck of a bottle filled with water, the bottle will burst, while its neck remains entire.

In the former case, the water is merely displaced, but not penetrated; while in the latter, it is forced through a solid substance, without yielding to the compression.

3. Bladders filled with water or air, and placed on a table, will support very large weights, set on a board which has been laid upon them.

The air, though it be compressible, and, in this respect, unlike water, yet resists absolute penetration; as will be obvious from the following experiment:

4. Take a large vessel nearly filled with water, and, on the surface of the water, place a lighted taper so as to float without being extinguished; if above this taper a glass tumbler be inverted, and pressed downwards, the contained air preserving its place, the middle of the water will descend, while the rest will rise up at the sides, and the taper will appear, for some seconds, to burn, although wholly encompassed by the liquid. The pressure may, indeed, be increased to any extent; but it will never cause the air wholly to disappear, although it may be contracted into a smaller space.