attained to great perfection. This also might be compared to an elephant's trunk, reaching entirely down to the surface of the water. At the bottom it was quite small, and it expanded pretty uniformly until it united with the mass of clouds above. It was nearly straight, but by no means upright in position; the top inclining about twenty degrees towards the south. Around its base there rose a vapor which had the appearance of smoke, spreading out on all sides, and rising to a height about onethird that of the trunk. This occurred about forty minutes past eight in the morning. In about five minutes the trunk had contracted so that it no longer reached the surface of the water, but was left dangling in the air like the one first seen. It was soon reduced to one half its former length, and the part which remained was expanded somewhat in breadth. It now appeared to have no connection with the water, except that the same smoky appearance was observed beneath it. The trunk continued to contract in length, and in about ten minutes from its first appearance, it was entirely gone. The same smoky appearance rising from the water in this vicinity was noticed about ten minutes afterwards, and was at first suspected to indicate the commencement of a third spout, but no column of cloud was seen connected with it, and it is possible that this was but the remains of the second spout. The wind continued fresh all day, with numerous flying clouds, but although a good watch was maintained, no further spouts were noticed. The clouds were chiefly of that variety called cumulus, rising in high massive piles and spreading out at the top like a mushroom.

It is difficult to estimate the dimensions of this spout, on account of the uncertainty with regard to its distance. It was presumed to have been distant about five or six miles from our boat, in which case the length of the column could not have been less than half a mile; its diameter at the top must have been more than twenty rods, and at the bottom about half as great. As the column contracted in length, its diameter at one time must have been nearly forty rods.

The distance of the spout was such that it was impossible to distinguish any clear signs of rotation; but from its analogy with other phenomena, it is presumed to have been a whirlwind, precisely like the little whirls which are so common on land. When a whirl is formed over a bed of sand, the dust is raised in the centre, and presents the appearance of a solid column which travels slowly along with the current in which it is formed. When the whirl passes over a large body of water, the water is raised in the form of spray; and the result is a column of water instead of a column of sand. The quantity of water thus elevated is probably extremely small, the column consisting of little more than dense fog or cloud. In the case just described, the whirl

was of very large dimensions, and rose to the height of the clouds, so that the spray elevated mechanically from the lake, was united with the condensed vapor of the clouds in the same column. The only danger therefore to be apprehended by a vessel from the passage of a water-spout, arises from the whirl, which often exhibits great violence. The whirlwind might prove destructive to a vessel, while the water which it carries with it might be barely sufficient to wet the deck.

ART. XXXIII.-On Certain Laws of Cohesive Attraction; by JAMES D. DANA.

Read before the American Association of Geologists and Naturalists, held at Boston, September, 1847.

FROM the account of cohesive attraction in works on Chemistry, we gather little more than what the term itself implies; and in the higher treatises on Physics, the subject is discussed on general mathematical principles, and mostly without reference to observed facts, excepting those of the most obvious character. This is especially true of the attraction in solidification. I propose to consider what observation teaches on this subject, and would ask the attention of the Association to a brief statement of a series of facts, and to certain obvious inferences from these facts.

*

The objects to which we appeal for illustration, are the rocks and minerals of the earth, and the ordinary forms of inorganic matter. The grand principle has already been recognized, that solidification and crystallization are the same process. As early as 1807, in the Lectures on Natural Philosophy by the learned Thomas Young, this philosopher says, after some explanatory remarks, "It appears, therefore, consistent both with reason and experience, to suppose that a crystallization more or less perfect is the universal cause of solidity." Biot in his Précist recognizes the same principle; and other names favoring this conclusion might be mentioned. The fact is obviously exemplified in nearly every inorganic solid around us. The freezing of water is known to be its crystallization, and snow is crystallized vapor. The coarse-grained structure of bar-iron is correctly called its crystalline structure; for the grains are all formed by the process of crystallization; and in steel we perceive the same texture, and may trace it through varieties, till the grains are too fine to be distinguished. Granite and all igneous rocks are made up of

*Course of Lectures on Natural Philosophy and the Mechanical Arts, by Thomas Young, M.D., 2 vols. 4to. London, 1807 Vol. i, p. 628.

Précis Elementaire de Physique, 2 vols. 8vo. Paris, 1824. Vol. i, p.

18.

crystallized material; and any one familiar with granite can pick out its mineral grains and exhibit their crystalline character; and if granite is crystallized in its intimate texture, so are all aggregate rocks made up of granite material. Indeed a general survey of the inorganic world develops the truth that here the power of crystallization rules, like vitality in the organic kingdoms. A crystalline texture may not always be apparent. This is the case internally with ice, or a fragment of quartz crystal, although there is no doubt that in each of these instances, the forces of crystallization were the cause of solidification. This is also true of the finest grained steel, as just observed, and some basaltic rocks. But we find, from the transitions in structure, that the apparent absence is owing to the extreme minuteness of the grains and the compactness of texture.

If then, crystallization and solidification are properly one and the same process, the laws that govern in crystallization are the laws of cohesive attraction. The science of crystals instead of treating only of certain singular polyhedral forms assumed by minerals, is the study of the fundamental agency by which inorganic matter is governed in its aggregations: and in place of occupying a short chapter in our text-books on physics, and there, as would often seem, in the way or out of place, it should be made to stand prominently forth as embodying and exemplifying some of the widest elemental truths of nature.

Let us then look at the facts, in order to arrive at these laws. Some of the deductions are by no means new. We commence with the simplest principles, in order to present a general view of the subject; and a few familiar facts in crystallography are illustrated with figures, as the subject may interest some who are not acquainted with them.

1. It is, in the first place, an established fact that the different kinds of inorganic matter have each a distinct mode of crystallization. Every species has certain fixed, determinate, angles, which characterize the structure, both of the crystal and the crystalline grains in a compact mass. Galena crystallizes with a cubical structure; and even in a granular mass, this structure may with care be detected by the rectangular cleavages. So in granular limestone, or common white marble, the oblique angles of the grains are precisely those of the perfect crystals of cale spar. As this is a general truth, these fixed angles, for each species of matter, in some way characterize molecular or cohesive attraction.

Again: crystals have plane surfaces, and are prisms or allied forms. Now if the attraction acted alike in every direction it would make only spheres; to produce polygonal forms there must, therefore, be specific directions in which the attraction acts more strongly than in others. For a cube or prism, there must be at least three such directions, corresponding with axes in the

form; and if the prism has oblique angles instead of being rectangular, these lines of strongest attraction must have a corresponding obliquity. Hence the angles referred to, as characterizing cohesive attraction, are angles between certain imaginary lines, or axes, in whose direction the attraction is strongest.

Again the crystalline forms in nature are well known to have fundamentally fixed relative dimensions, indicated by the modifications they undergo (producing secondary forms) though not necessarily apparent in the actual proportions of the crystal. Thus a cube, which is equal in its dimensions, shows it in all its modifications; and in a prism, the inequality in the dimensions is as exactly and precisely indicated by its modifications.* The relative dimensions belonging to the fundamental form of a substance, are often therefore easily calculated; and the whole science of crystals is thus based on rigorous mathematical laws.

From these facts we may conclude therefore with respect to solids, that Cohesive Attraction is characterized by fixed angles, as regards the direction of its action, and by specific relations of force in certain axial directions; and it differs in these particulars for different substances.†

These facts are the only hints which nature gives us respecting the axial dimensions of molecules. We proceed on the only possible grounds for any conclusion on this point, when we infer that molecules have corresponding relative dimensions with the crystalline forms, and the same specific angles between the funda

*

A square prism and a cube as presented in nature, may have actually the same dimensions, owing to the distortion of the one or the other. But the fundamental nature of their forms, may, notwithstanding, be obvious to the eye. In the cube (having equal faces and axes) all the edges will have similar secondary planes (that is, these planes will be identical in their inclinations to the faces of the cube); in the prism, the secondary planes of the lateral edges will differ in their inclinations from those of the terminal. In the cube, there may be a plane on any edge equally inclined to the faces of the cube. In the prism, the plane on a terminal edge will always be unequally inclined to the including faces; such a plane removes a part of the two including faces, and these parts will in all cases have a definite relation to the height and breadth of the prism. These explana tions are sufficient to render the general principle stated, intelligible to those unacquainted with the structure of crystals. Treatises on crystals should be studied for a full exposition of this subject.

↑ Apparent exceptions to this principle are supposed to exist in the case of glass, tabasheer and some other substances that do not polarize light. They are, however, not necessarily exceptions. For in these substances the molecules are either cquiaxal or inequiaxal ;—if inequiazal, the solids prove that such molecules, with weak polar forces, may be so irregularly aggregated as to show no polarization; and if their form is equiaxal, no rings of polarization are to be expected.

We have no facts to determine the form of the molecules in glass. As glass, (common as well as volcanic,) when slowly cooled, produces a different material, with a different temperature of fusion, it must be a dimorphous or isomerous material, capable of taking two distinct forms, of which glass is one. We cannot, therefore, infer that the molecules of glass are inequiaxal from the forms of the crystallized silicates of an alkali. The rapid cooling, necessary to form glass, is the most unfavorable for an axial arrangement of the particles, even if the polar forces were strong.

mental axial lines or axes of attraction. Thus the molecule of a cube must have equal axes, like the cube itself; that of a prism, like axes with the prism in relative dimensions; and if oblique, the axes should have the same degree of obliquity. This statement with regard to molecules is potentially true; and in this sense, the only one in which we now speak of molecules at all, it is no hypothesis.

The actual forms of molecules constitute another consideration, and one for which we have less precise data. The molecule of a cube may be either a sphere or a cube, as either form would produce a cube by the same mode of aggregation; and that of a prism may be either a similar prism or a spheroid of like dimensions. This is illustrated in the annexed figures 1, 2, 3. Fig. 1. Fig. 2.

Fig. 3.

We cannot therefore determine absolutely the form of the molecule from the form of the crystal. But from the greater simplicity of the hypothesis that molecules are spheres and spheroids, its sufficiency to meet every case in nature, its necessity to explain optical phenomena, and other considerations we have presented elsewhere, we adopt in this place the view of their spheroidal forms.

By having some idea of a molecule in the mind, we may more easily conceive of the principles deduced with regard to cohesive or molecular attraction.

Our first inference, expressed with reference to the molecule will therefore be the following:

I. Molecules in solids have fixed relative dimensions for each kind of matter, and certain axial lines of cohesive attraction which are fixed in direction :—and we add, as a necessary truth, whose force is inversely related to their length.

Viewing the molecules as spheres and spheroids, the three axes are the three conjugate axes or conjugate diameters of these forins.* The attraction is not supposed to be confined to the

*If the conclusion be correct that the molecule of the clement gold is a simple sphere because of its cubical crystals; and that of sulphur an ellipsoid, from the unequal axes of its crystals;-it is as good also with regard to compounds. Hence the molecule of pyrites (a compound of sulphur and iron), whose crystal is a cube must be a sphere; and that of alum, a spheroid, &c. It matters not whether we can conceive or not of two molecules of sulphur and one of iron, different in size and shape, uniting so as to make a simple sphere. The conclusion is one not dependent for its truth on our conceptions. The finite mind is an interpreter of nature and may not presume to the rank of dictator. Its conceptions will be as inane with regard to any kind of combination or mode of aggregation in the above case, which could produce out of such means a symmetrical cube with its faces similar in lustre and every other physical character.