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body, what proportion the increase of Friction bears to the increase of weight.

3dly, The smallest surface has the least Friction; the weight being the same. But the ratio of the Friction to the surface is not yet accurately known.

Mr. Vince's experiments consisted in determining how far the sliding bodies would be drawn, in given times, by a weight hanging freely over a pulley. This method would both shew him if the Friction were a constant retarding force, and the other conclusions above stated. For as the spaces described by any constant force, in given times, are as the squares of the times; and as the weight drawing the body is a constant force, if the Friction, which acts in opposition to the weight, should also be a constant force, then their difference, or the force by which the body is urged, will also be constant, in which case the spaces described ought to be as the squares of the times; which happened accordingly in the experiments.

Mr. Vince adds some remarks on the nature of the experiments which have been made by others. These, he observes, the authors “have instituted, To find what moving force would just put a body at rest in motion: and they concluded from thence, that the accelerative force was then equal to the Friction; but it is manifest, that any force which will put a body in motion must be greater than the force which opposes its motion, otherwise it could not overcome it; and hence, if there were no other objection than this, it is evident, that the Friction could not be very accurately obtained; but there is another objection, which totally destroys the experiment, so far as it tends to shew the quantity of Friction, which is the strong cohesion of the body to the plane when it lies at rest.” This he confirms by several experiments, and then adds, “From these experiments therefore it appears, how very considerable the cohesion was in proportion to the Friction when the body was in motion; it being, in one case almost <*>/3, and in another it was found to be very nearly equal to the whole Friction. All the conclusions therefore deduced from the experiments, which have been instituted to determine the Friction from the force necefsary to put a body in motion (and I have never seen any described but upon such a principle) have manifestly been totally false; as such experiments only shew the resistance which arises from the cohesion and Friction conjointly.” Philos. Trans. vol. 75, pa. 165.

Mr. Emerson, in his Principles of Mechanics, deduces from experiments the following remarks relating to the quantity of Friction: When a cubic piece of soft wood of 8 pounds weight, moves upon a smooth plane of soft wood, at the rate of 3 feet per second, its Friction is about 1/3 of the weight; but if it be rough, the Friction is little less than half the weight: on the same supposition, when both the pieces of wood are very smooth, the Friction is about 1/4 of the weight: the Friction of soft wood on hard, or of hard wood upon soft, is 1/5 or 1/6 of the weight; of hard wood upon hard wood, 1/7 or 1/<*>; of polished steel moving on steel or pewter, 1/4; moving on copper or lead, 1/<*> of the weight. He observes in general, that metals of the same sort have more Friction than those of different sorts; that lead makes much resistance; that iron or steel running in brass makes the least Friction of any; and that metals oiled make the Friction less than when polished, and twice as little as when unpolished. Desaguliers observes that, in M. Camus's experiments on small models of sledges in actual motion, there are more cases in which the Friction is less than where it is more than 1/3 of the weight. See a table, exhibiting the Friction between various substances, formed from his experiments in Desag. Exp. Philos. vol. 1, p. 193 &c. also p. 133 to 138, and p. 182 to 254, and p. 458 to 460. On the subject of Friction, see several vols. of the Philos. Trans. as vol. 1, p. 206; vol. 34, p. 77; vol. 37, p. 394; vol. 53, p. 139, &c.

FRIDAY

, the 6th day of the week, so called from Friga, or Friya, a goddess worshipped by the Saxons on this day. It is a fast-day in the church of England, in memory of our Saviour's crucisixion, unless Christmas-day happen to fall on Friday, which is always a festival.

Good Friday, the Friday next before Easter, representing the day of our Saviour's crucifixion.

FRIGID Zone, the space about either pole of the earth to which the sun never rises for one whole day at least in their winter. These two zones extend to about 23 1/2 degrees every way from the pole, as their centre.

FRIGORIFIC

, in Physics, something belonging to, or that occasions cold.—Some philosophers, as Gassendus, and other corpuscularians, denying cold to be a mere privation, or absence of heat, contend that there are actual Frigorific corpuscles or particles, as well as fiery ones: whence proceed cold and heat. But later philosophers allow of no other Frigorific particles beside those nitrous salts &c, which float in the air in cold weather, and occasion freezing.

FRIZE

, Frieze, or Freeze, in Architecture, a part of the entablature of columns, between the architrave and cornice.

FRONT

, in Architecture, denotes, the principal face or side of a building; or that presented to their chief aspect and view.

Front

, in Perspective, a projection or representation of the face, or forepart of an object, or of that part directly opposite to the eye, called also more usually orthography.

FRONTISPIECE

, in Architecture, the portale, or principal face of a fine building.

FRONTON

, in Architecture, an ornament among us more usually called Pediment.

FROST

, such a state of the atmosphere as causes the congelation or freezing of water or other fluids into ice.

The nature and effects of Frost in different countries, are mentioned under the articles Congelation, and Freezing. In the more northern parts of the world, even solid bodies are affected by Frost, though this is only or chiefly in consequence of the moisture they contain, which being frozen into ice, and so expanding as water is known to do when frozen, it bursts and rends any thing in which it is contained, as plants, trees, stones, and large rocks. Some fluids expand by Frost, as water, which expands about <*>th part, for which reason ice floats in water; but others again contract, as quicksilver, and hence frozen quicksilver sinks in the fluid metal.

Frost, being derived from the atmosphere, naturally proceeds from the upper parts of bodies downwards, as the water and the earth: so, the longer a Frost is