so continues for two or three days before the foul weather is quite over, then expect a continuance of fair weather to follow.

6. In fair weather, when the mercury falls much and low, and thus continues for two or three

days before the rain comes, then expect a great deal of wet, and, probably, high winds.

7. The unsettled motion of the mercury denotes uncertain and changeable weather.

8. You are not so strictly to observe the words engraven on the plates, as the mercury's rising and falling; though, in general, it will agree with them. For if it stands at much rain, and then rises up to changeable, it presages fair wea ther; though not to continue so long as if the mercury had risen higher. And so, on the contrary, if the mercury stood at fair, and falls to changeable, it presages foul weather; though not so much of it as if it had sunk lower.

M. Chiminello observed the ba rometer twenty-two times a day for three years, but he left a chasm in the night which he supplied by calculation, The principal posi tions which he thence deduced are, that the barometer falls to wards noon, as well as towards night.

M. Hemmer, from a great num. ber of accurate observations, deduced the three following general rulés :

Mr. Patrick's Rules. These are esteemed the best of any general rules hitherto made : 1. The rising of the mercury presages, in general, fair weather; and its falling, foul weather, as rain, snow, high winds, and storms. 1st. When the sun passes the 2. In very hot weather, the fall-meridian, the barometer, if in the ing of the mercury indicates thun-act of falling, continues to fall. der. and the falling is accelerated.

3. In winter, the rising presages frost and in frosty weather, if the mercury falls three or four divisions, there will certainly follow a thaw. But in a continued frost, if the mercury rises, it will certainly

snow.

4. When foul weather happens soon after the falling of the mercury, expect but little of it; and, on the contrary, expect but| little fair weather when it proves fair shortly after the mercury has risen.

5. In foul weather, when the mercury rises much and high, and 78

2d. When the sun passes the me. ridian, the barometer, if in the act of rising, falls, or becomes stationary, or rises more slowly.

3. When the sun passes the meridian, the barometer, which is stationary, falls, if it has not risen before or after being stationary ; in which case it usually becomes stationary during the sun's passage.

BAROSCOPE, an instrument intended only to show that the air has weight; whereas the barometer measures that weight, and determines its true quality.

BARREL, an English vessel or

at once. Dr. Priestley describes a still more complete battery: this consists of 64 jars, each 10 inches long, and 2 inches in diameter, all coated within an inch and a half of the top, forming in the whole about 32 square feet of coated surface. But the largest and most powerful battery of all is that employed by Dr. Van Marum, to the electrical machine, constructed for Teyler's museum at Haarlem. This grand battery consists of a great number of jars coated as above, to the amount of about 130 square feet; and the effects of it, which are truly astonishing, are related by Dr. Van Marum in his description of this machine, and of the experiments made with it at Haarlem, 1785.

most piece of silver with the other, a shock will pass through the arms, which will be strong in proportion to the number of pieces of zinc &c. employed." Of late, copper has been used instead of silver, on account of its being cheaper; and solutions of muriate of ammonia (sal ammoniac,) of nitrous acid, and of muriatic acid, have been substituted for the solution of common salt, with increased effect. Any two metallic substances, which are perfect conductors of electri city, will answer the purpose, on condition that the interposed fluid is capable of oxidizing at least one of them.

that of exciting the muscular energy in a subject recently dead in the ratio of the number of combi nations. Very powerful batteries have been made with concentric cylinders of zinc and copper. See Galvanism.

The galvanic trough consists of a box of baked wood, in which plates of copper and zinc, or of Galvanic BATTERY, or Pile, an silver and zinc, soldered together apparatus employed for accumu- at their edges, are cemented in lating galvanism. It was invented such a manner as to leave a num by Volta, from whose labours the ber of water-tight cells correspondscience of galvanism derived manying to the number of the series. advantages and much improve- Piles and batteries of various ment. Mr. Henry, in his valuable forms and powers have been conEpitome of Chemistry, gives the structed by different experimenfollowing easy directions for the talists. It has been found that the construction of this pile: "Pro-power of chemical decomposition cure, at a brazier's or copper-is in the ratio of the surfaces, and smith's, 30, 40, or 50 pieces of zinc or speltre, cast in sand, of the size of half-crowns or shillings, but rather thicker. A corresponding number of half-crowns or shillings will also be required, according to the sizes of the pieces of zinc that may be employed. Let an equal BEARD of a Comet, the rays number of pieces of woollen cloth which it emits in the direction in be cut, of a circular shape, to cor- which it moves, as distinguished respond with the pieces of zinc, from the tail, or the rays emitted and steep these in a strong solution or left behind it as it moves along. of common salt in water. Then BEARING, in Geography and dispose the three substances alter-Navigation, the position of one nately, in the following order: place with regard to another, as silver, zinc, moistened cloth; sil-estimated by the points of the com ver, zinc, &c. till a sufficient num-pass. ber of these triplicates, not less BELTS, zones or girdles, surthan 20 or 30, have been thus ar- rounding the planet Jupiter, more ranged, the silver terminating the lucid than the other parts of his pile at top. In order to facilitate body, and terminated by parallel the touching of the bottom piece straight lines, being sometimes of silver, it may be well to put broader and sometimes narrower, under it a slip of tinfoil, or Dutch varying both in magnitude and leaf, which may project a few in- position. ches. Next, let the hands be BENDING, the reducing a body moistened with salt and water, to a curved or crooked form. The and, on touching the piece of tin-bending of boards, planks, &c. is foil with one hand, and the upper-effected by means of heat, usually

by boiling, by which their fibres are so relaxed that they may be bent into any figure at pleasure.

=1, or an-1=0; the solution of which forms one of the most interesting researches of the modern BEVEL Angle, is a term used by algebra. It is obvious, that if we artificers to denote any angle ex- have n=1, where n is a prime cept those of ninety or forty-five number; and also xnm=1, that the degrees. Bevel is also the name roots of the former equation are of an instrument used by workmen likewise roots of the latter. For in setting off angles. let r, s, t, &c. be the roots of the BILLION, in Numeration, a mil-equation an=1, so that rn = 1, sn= lion of millions, or 10000-0000-0000; 1, &c.; then it is evident also that The French mathematicians un-nm=1, snm=1, &c. and, consederstanding billion to mean thou-quently, the roots of the former sands of millions, and the English are, at the same time, roots of the millions of millions; thus, with the latter. French, the place of billions is said to be the tenth from the right=0, n being a prime number, there In every binomial equation, an — 1 towards the left, whereas we make are contained one real root, and nit in our arithmetics the thir-1 imaginary roots, which latter are BIMEDIAL Line, in Geometry, different from each other, the sum all powers of each other, and all is the sum of two medials. Thus, of which is equal to their continued when two medial lines, commen-product, being both equal to -1. surable only in power, and containing a rational rectangle, are roots as their units in the index of Every equation having as many compounded, the whole shall be its highest power, it is evident that irrational with respect to either of the whole number of roots is n, the two; and is called, by Euclid, a first bimedial line. But if two medial lines, commensurable only in power, and containing a medial rectangle, be compounded, the whole will be irrational; and is called a second bimedial line.

teenth.

BINARY Number, is a number consisting of two units.

BINARY Arithmetic, or BINARY Scale of Notation. See Arithmetic. BINOCULAR Telescope, is a telescope to which both eyes may be applied. It consists of two tubes, with two sets of glasses of the same power, and adjusted to

the same axis.

and of these only one can be real, viz. x=1; consequently, all the. other n-1 roots are imaginary, and that they are all powers of each other may be shown as fol

lows:

Let r represent any one of these imaginary roots, then since rn=1, so likewise will r2=1, r&n=1, in 1, &c.; therefore, ifr be one root, so likewise is every term in the series r, r2, r3, r1, &c. rn~! for each of these quantities raised to the nth power is equal to unity, which is the condition of the equa tion. Whence it follows, that any one of these roots may be considered as the leading one in the series, and all the others will still be powers of this, and of each other.

BINOMIAL, in Algebra, a quantity consisting of two terms or names, and connected by the signs +plus,-minus, or = equal; thus, a + b, a — b, a = b, are all binoThese roots are also all different. mials; the difference a - - b, being For let rearga, where p and q also frequently called a residual; are each necessarily less than n, Thus we say, Binomial Curve, and since by the supposition pand Equation, Surd, Theorem, &c. BINOMIAL Curve, is a q are not equal, let p>q, then curve dividing the equation parga by whose ordinate is expressed by arqa, we have r(9)a 1, so that binomial quantity; as, for instance, r(p-q)a would likewise be a root y=xm√b+dxn. of the same equation, but this is impossible; no two of the series of roots are equal to each other.

BINOMIAL Equation, is any equation of two terms, but more commonly applied to the higher order of equations of the form an

It follows also, from the known theory of equations, that the sum

of all the roots is equal to the co

efficient of the second term, which an-288+ un-sf3, in the present case is 0; and that &c. where the law of the series is the continued product is equal to immediately obvious. Thus, the absolute term, which is here (a+b)3=a3+3a2b+3ab2+bs