Attwood, George

a distinguished English physicist, в. 1745; D. 1807. He is known by his treatise on the Rectilinear Motion and Rotation of Bodies; but principally by a mechanical contrivance known as Attwood's Machine, the principle of which merits some notice. Perhaps no questions in mechanics are more interesting than those concerning IMG:content-0411.png:[blocks in formation] weight B , with the bar upon it, be allowed to fall, it will be found that the force of gravity will pull it down one inch during one second. Now, adjust the shelf C, BO that the bar shall be removed at the end of the first second; it will then be found that the weight will fall two inches the next second. At the end of the first second, then, the weight is projected vertically downward, with a velocity of two inches per second. If now the bar is left on during both seconds, the weight will be found to have fallen three inches during the 2d second. Hence, the force of gravity pulls the weight down the 2d second an inch further than its velocity at the beginning of this second would have carried it; that is, just as low as gravity would have pulled it from a state of rest. - By means of this same machine the case of a body projected vertically upward can be illustrated. While one of the weights is falling, the other weight is rising. Suppose that one bar be placed upon the ascending weight, and two on the descending weight; the second a little heavier than the first, so that it shall bear the same ratio to the whole weight now as the one bar used at first. We have already seen that this bar, acting during one second, will give one of the weights a velocity downward of two inches every second, and the other weight the same velocity upward. Suppose now that at the end of the first second both bars be caught off the descending weight, the other weight will rise not two inches, but only one during the next second. Had it not been for the action of gravity upon the bar resting on it, it would have risen two inches. But we have already seen that gravity acting upon this bar will cause the weight to fall one inch from a state of rest; hence it is pulled just as far from the place it would have reached as it would have been pulled from a state of rest. - See GRAVITY, MOTION, . Atu'res, a town of S. America, in Venezuela, on the Orinoco, 105 m. N.N.E. of San Fernando. At'water, in Ohio, a post-township of Portage co., 12 m. S. by E. of Ravenna. Atweel', interj. [0. Eng., I wot well.] Very well. (Scottish.) Atwist', adv. [Prefix a, and twist.] Awry; twisted; distorted. (R.) At'wood, in Indiana , a post-office of Kosciusko co. Atwood, in Michigan , a post-office of Antrim co. At'wood's Key, a small island of the W. Indies, in the Bahama group, 33 m. N. by E. of Acklin Island; Lat. 23° 5' N.; Lon. 73° 43′ W. Atyp'ic, a . [Gr. a , priv., and typos , type.] ( Med . ) That which has no type; irregular; chiefly applied to an irregular intermittent. Atyp'us, n . ( Zool .) A genus of spiders-the species of which inhabit turfy declivities, where they form deep cylindrical excavations seven or eight inches long. In these they weave a kind of funnel of white silk of the same dimensions, and at the bottom of this cavity the cocoon in which their eggs are deposited is fixed by means of threads attached to each other. Au, the name of a small town of Hungary, and of several villages in Germany. Aubagne', ( ō - ban ' , ) a town of France, dep. of Bouchesdu-Rhone, 10 m. E. of Marseilles, on the railway to Nice. It is divided into an old and a new town. The former is mean, and the latter well-built, supporting the fabrication of earthenware, paper, . Population 7,232.