Page:Supplement to the fourth, fifth, and sixth editions of the Encyclopaedia Britannica - with preliminary dissertations on the history of the sciences - illustrated by engravings (IA gri 33125011196181).pdf/937

 ''in the year 1801; and containing Propositions for Determining the weights of the several sections which constitute an arch, inferred from the angles. Also containing a Demonstration of the angles of the several sections, when they are inferred from the weights thereof. To which is added, a Description of original experiments to verify and illustrate the principles in this treatise. With occasional remarks on the construction of an iron bridge of one arch, proposed to be erected over the river Thames at London. Part II. By the author of the first part''. 4to, Lond. 1804. Dated 24th Nov. 1803.

11. A Treatise on Optics is mentioned by Nichols as having been partly printed by Bowyer in 1776, but never completed.

It may be very truly asserted, that several of these works of Mr Atwood have materially contributed to the progress of science, by multiplying the modes of illustration, which experimental exhibitions afford for the assistance of the instructor; at the same time, they can scarcely be said to have extended very considerably the bounds of human knowledge, or to demonstrate that their author was possessed of any extraordinary talent or energy of mind in overcoming great difficulties, or in inventing new methods of reasoning. The Analysis of a Course of Lectures has been little read: and it bears evident marks of having been composed before Mr Atwood had acquired a habit of accurate reasoning on Physical subjects. In the first page, for example, the forces of cohesion and gravitation are completely confounded; and in the third we find the idea of perfect spheres touching each other in a greater or less number of points, notwithstanding the appearance of precision which the author attempts to maintain in his language.

The object of the paper on Reflection is, to illustrate and improve the construction of Hadley’s quadrant; and Mr Atwood proposes, for some particular purposes in practical Astronomy, two new arrangements of the speculums, by which the rays are caused to move in different planes, and which he considers as affording greater accuracy for the measurement of small angles than the common form of the instrument, although not of general utility, nor very easily adjusted for observation.

The treatise on Rectilinear motion and rotation exhibits a good compendium of the elementary doctrines of mathematical Mechanics; but it shows a great deficiency in the knowledge of the higher refinements which had been introduced into that science by Daniel Bernoulli, and Euler, and Lagrange. The properties of simply accelerated and retarded motion are first discussed, and the phenomena of penetration experimentally examined; the laws of varying forces are then investigated, and the properties of the pendulum demonstrated; the vibrations of an elastic chord are calculated, “considering the whole mass to be concentrated in the middle point,” as an approximation; and then, instead of imitating and simplifying the elegant but complicated demonstrations of the continental mathematicians, the author most erroneously repeats, in the words of Dr Smith, the exploded doctrine, that “the string, during any instant of its vibration, will coincide with the harmonic curve.” The subject of a resistance, varying as the square of the velocity, is next examined; and some useful experiments on the descent of bodies in water are stated in confirmation of the theory. On this occasion, the author observes, with regard to the formation of the different strata of the earth, that bodies disposed to break into large masses, though specifically lighter, may easily have descended more rapidly through a fluid, than denser but more brittle bodies, so that the natural order of densities may thus have become inverted. He next examines the theory of rotation, and relates some very interesting experiments on rectilinear and rotatory motions; and he shows that Emerson and Desaguliers were totally mistaken in asserting “that the momentum produced is always equal to the momentum which produces it.” The last section of the work, which is devoted to the subject of free rotation, is the most elaborate of the whole; but it exhibits no material extension of the earlier investigations of the Bernoullis and Professor Vince; nor does it contain the important proposition of Segner, relating to the existence of three axes of permanent rotation, at right angles to each other, in every body, however irregular.

Notwithstanding these partial objections, the work may still, in many respects, be considered as classical. The paper on Watch-balances is principally intended to show the advantages which may be obtained, in Mr Mudge’s construction, from the effect of subsidiary springs in rendering the vibrations isochronous, their actions being limited to certain portions of the arc of motion. If the author has here again omitted to follow the Continental Mathematicians in some of their refinements of calculation, it must be confessed that his view of the subject has, lt this instance, not only the advantage of simplicity, but also that of a nearer approach to the true practical state of the question, than is to be found in the more complicated determinations which had been the result of the labours of some of his predecessors.

But, whatever may be the merits of these investigations, they appear to be far exceeded in importance by the papers on Ships, the first of which obtained for its author the honour of a Copleian Medal. Its principal object is to show how much the stability of a ship will commonly vary, when her situation, with respect to the horizon, is materially altered; and how far the assumptions of theoretical writers, respecting many others of the forces concerned in Naval Architecture, will generally differ from the true state of these forces when they actually occur in Seamanship. In the second part of the investigation, some errors of Bouguer and of Clairbois are pointed out, and the theoretical principles of stability are exemplified by a detailed calculation, adapted to the form and dimensions of a particular vessel, built for the service of the East India Company.

The latter years of our author’s life do not appear to have been productive of any material advantage to Science. His application to his accustomed pursuits was unremitting; but his health was gradually declining. He had no amusement, except such as was afforded by the continued exercise of his mind, with