act on a calorific medium: they are the cause of the production of heat, by uniting with the matter of fire which is contained in the substances that are heated; as the collision of the flint and steel will inflame a magazine of gunpowder, by putting all the latent fire which it contains into action. On the tops of mountains of sufficient height, at the altitude where clouds can seldom reach to shelter them from the direct rays of the sun, we always find regions of ice and snow. Now, if the solar rays themselves conveyed all the heat we find on this globe, it ought to be hottest where their course is the least interrupted. Again, our aëronauts all confirm the coldness of the upper regions of the atmosphere; and since, therefore, even on our earth, the heat of the situation depends upon the readiness of the medium to yield to the impression of the solar rays, we have only to admit, that on the sun itself the elastic fluids composing its atmosphere, and the matter on its surface, are of such a nature as not to be capable of any extensive affection of its own rays; and this seems to be proved by the copious emission of them; for if the elastic fluids of the atmosphere, or of the matter contain ed on the surface of the sun, were of such a nature as to admit of an easy chemical combination with its rays, their emission would be very much impeded. Another well known fact is, that the solar focus of the largest lens thrown into the air will occasion no sensible heat in the place where it has been kept for a considerable time, although its power of exciting combustion, when proper bodies are exposed, should be sufficient to fuse the most refractory substances.

It is by analogical reasoning that we consider the moon as inhabited. For it is a secondary planet of considerable size, its surface is diversified like that of the earth with bills and vallies. Its situation with respect to the sun is much like that of the earth; and by a rotation on its axis it enjoys an agreeable variety of seasons, and of day and night. To the moon our globe would appear a capital satellite, undergoing the same changes of illumination as the moon does to the earth. The sun, planets, and the starry constellations of the heavens, will rise and set there as they do here: and heavy bodies will fall on the moon as they do on the earth. There seems, then, only to be wanting, in order to complete the analogy, that it should be inhabited like the earth. It may be objected, that, in the moon, there are

no large seas; and its atmosphere (the existence of which is doubted by many) is extremely rare, and unfit for the pur. poses of animal life; that its climates, its seasons, and the length of its days and nights, totally differ from ours; that without dense clouds, which the moon has not, there can be no rain, perhaps no rivers and lakes. In answer to this it may be observed, that the very difference between the two planets strengthens the argument. We find, even on our own globe, that there is a most striking dissimilarity in the situation of the creatures that live upon it. While man walks on the ground, the birds fly in the air, and the fishes swim in the water. We cannot surely object to the conveniencies afforded by the moon, if those that are to inhabit its regions are fitted to their conditions as well as we on this globe of ours. The analogy already mentioned establishes a high probability that the moon is inhabited.

Suppose, then, an inhabitant of the moon, who has not properly considered such analogical reasonings as might induce him to surmise that our earth is inhabited, were to give it as his opinion, that the use of that great body, which he sees in his neighbourhood, is to carry. about his little globe, in order that it may be properly exposed to the light of the sun, so as to enjoy an agreeable and useful variety of illumination, as well as to give it light by reflection, when direct light cannot be had, should we not condemn his ignorance and want of reflection? The earth, it is true, performs those offices which have been named for the inhabitants of the moon, but we know that it also affords magnificent dwellingplaces to numberless intelligent beings. From experience, therefore, we affirm, that the performance of the most salutary offices to inferior planets is not inconsistent with the dignity of superior purposes; and in consequence of such analogical reasonings, assisted by telescopic views which plainly favour the same opinion, we do not hesitate to admit that the sun is richly stored with inhabitants.

This way of considering the sun is of the utmost importance in its consequences. That stars are suns can hardly admit of a doubt. Their immense distance would effectually exclude them from our view, if their light were not of the solar kind. Besides, the analogy may be traced much further; the sun turns on its axis; so does the star Algol; so do the stars called

Lyra, Cephei, Antinoi, o Ceti, and

many more, most probably all. Now from what other cause can we, with so much probability, account for their periodical changes? Again, our sun's spots are changeable; so are the spots on the star o Ceti. But if stars are suns, and suns are inhabitable, we see at once what an extensive field for animation opens to our view.

It is true, that analogy may induce us to conclude, that since stars appear to be suns, and suns, according to the common opinion, are bodies that serve to enligh. ten, warm, and sustain a system of planets, we may have an idea of numberless globes that serve for the habitation of living creatures. But if these suns themselves are primary planets, we may see some thousands of them with the naked eyes, and millions with the help of telescopes; and, at the same time, the same analogical reasoning still remains in full force with regard to the planets which these suns may support. See Philosophical Transactions, and Young's Natural Philosophy.

We shall conclude this article with some particulars respecting the sun, by Sir Isaac Newton. 1. That the density of the sun's heat, which is proportional to his light, is 7 times as great in Mercury as with us, and that water there would be all carried off in the shape of steam; for he found, by experiments with the thermometer, that a heat seven times greater than that of the sun's beams in summer will serve to make water boil. 2. That the quantity of matter in the sun is to that in Jupiter nearly as 1100 to 1, and that the distance of that planet from the sun is in the same ratio to the sun's semidiameter; consequently, that the centre of gravity of the sun and Jupiter is nearly in the superficies of the sun. 3. That the quantity of matter in the sun is to that in Saturn as 2360 to 1, and that the distance of Saturn from the sun is in a ratio but little less than that of the sun's semidiameter. And hence the common centre of gravity of Saturn and the sun is a little within the sun. 4. By the same method of calculation it will be found, that the common centre of gravity of all the planets cannot be more than the length of the solar diameter distant from the centre of the sun. 5. The sun's diameter is equal to 100 diameters of the earth, and therefore its magnitude must exceed that of the earth one million of times. 6. If 360 degrees (the whole ecliptic) be divided by the quantity of the solar year, it will give 59′8′′, which

therefore is the medium quantity of the sun's apparent daily motion; hence his horary motion is equal to 2' 27". By this method the tables of the sun's mean motion are constructed as found in astronomical books.

SUPERCARGO, a person employed by merchants to go a voyage, and oversee their cargo of lading, and dispose of it to the best advantage.

SUPERFICIES, or SURFACE, in geometry, a magnitude considered as having two dimensions; or extended in length and breadth, but without thickness or depth. In bodies, the superficies is all that presents itself to the eye. A superficies is chiefly considered as the external part of a solid. When we speak of a surface simply, and without any regard to body, we usually call it figure. The several kinds of superficies are as follow: rectilinear superficies, that comprehended between right lines; curvilinear superficies, that comprehended between curve lines; plane superficies, is that which has no inequality, but lies evenly between its boundary lines; convex superficies, is the exterior part of a spheri cal or spheroidical body; and a concave superficies, is the internal part of an orbicular or spheroidical body.

The measure or quantity of a superficies, or surface, is called the area thereof.

The finding of this measure, or area, is called the quadrature thereof.

To measure the surfaces of the several kinds of bodies, as spheres, cubes, parallelopipeds, pyramids, prisms, cones, &c.

SUPERFICIES, line of, a line usually found on the sector, and Gunter's scale, the description and use whereof, see under SECTOR, and GUNTER's scale.

SUPERLATIVE, in grammer, one of the three degrees of comparison, being that inflection of nouns. adjective that serves to augment and heighten their signification, and shows the quality of the thing denoted to be in the highest degree.

SUPERNUMERARY, something over and above a fixed number. In several of the offices are supernumerary clerks, to be ready on extraordinory occasions. There are also supernumerary surveyors of the excise, to be ready to supply va cancies when they fall; these have but half pay.

SUPERSEDEAS, a writ that lies in a great many cases, and signifies, in ge neral, a command to stay proceedings,

on good cause shown, which ought other wise to proceed. By a supersede as, the doing of a thing, which might otherwise have been lawfully done, is prevented; or a thing that has been done, is (notwithstanding it was done in a due course of law) thereby made void. A supersedeas is either expressed or implied; an express supersedeas is sometimes by writ, sometimes without a writ; where it is by writ, some person, to whom the writ is directed, is thereby commanded to forbear the doing something therein mentioned; or, if the thing has been already done, to revoke, as that can be done, the act.

A person is superseded out of prison, when, by the practice of the court, the plaintiff has omitted to proceed in due time against him.

SUPPLEMENT of an arch, in geometry, or trigonometry, is the number of degrees that it wants of being an entire semicircle; as a complement signifies what an arch wants of being a quadrant.

SUPPORTED, in heraldry, a term applied to the uppermost quarters of a shield when divided into several quarters, these seeming as it were supporten or sustained by those below. The chief is said to be supported when it is of two colours, and the upper colour takes up two-thirds of it. In this case it is supported by the colour underneath.

SUPPORTERS, in heraldry, figures in an achievement placed by the side of the shield, and seeming to support or hold up the same. Supporters are chiefly figures of beasts: figures of human creatures, for the like purpose, are properly called tenants. Some make another difference between tenant and supporter: when the shield is borne by a single animal, it is called tenant; when by two, they are called supporters. The figures of things inanimate, sometimes placed aside of escutcheons, but not touching or seeming to bear them, though sometimes called supporters, are more properly cotises. The supporters of the British arms are a lion and an unicorn. In England, none under the degree of a banneret are allowed supporters, which are restrained to those called the high nobility. The Germans permit none but princes and noblemen of rank to bear them; but among the French, former ly, the use of them was more promis

cuous.

SUPPRESSION, in grammar and rheVOL. XI.

toric, denotes an omission of certain words in a sentence, which yet are necessary to full and perfect construction: as, "I come from my father's;" that is, "from my father's house." Suppression is a figure of speech very frequent in our language, chiefly used for brevity and elegance. Some rules relating thereto are as follow: 1. Whenever a word comes to be repeated in a sentence oftener than once, it is to be suppressed. Thus, we say, "This is my master's horse," not " This horse is my master's horse." 2. Words that are necessarily supplied may be suppressed: and, 3. All words that use and custom suppress in other languages, are also to be suppressed in English, unless there be particular reasons for the contrary.

Suppression is also a figure in speech, whereby a person in rage, or other disturbance of mind, speaks not out all he means, but suddenly breaks off his discourse. Thus the gentleman in Terence, extremely incensed against his adversary, accosts him with this abrupt saying, "Thou of all." The excess of his indignation and rage choked the passage of his voice, and would not suffer him to utter the rest. But in these cases, though the discourse is not complete, the meaning is readily understood, and the evidence of the thought easily supplies the defect of words. Suppression sometimes proceeds from modesty, and fear of uttering any word of ill and offensive sound.

SURD, in arithmetic and algebra, denotes any number or quantity that is ined an irrational number or quantity. commensurable to unity; otherwise call

The square roots of all numbers, except 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, &c. (which are the squares of the integer numbers, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, &c.) are incommensurables: and after the same manner the cube roots of all numbers, but of the cubes of 1, 2, 3, 4, 5, 6, &c. are incommensurables; quantities that are to one another in the proportion of such numbers must also have their square roots, or cube roots, incommensurable.

and

The roots, therefore, of such numbers, being incommensurable, are expressed by placing the proper radical sign over them: thus 2/2, 2/3, 25, 26, &c. express numbers incommensurable with unity. However, though these numbers are incommensurable themselves with 0 0