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/26

xviii Astronomy forms the subject of one of the most extensive treatises in the Encyclopædia, nd nothing has been added, in the present work, upon the descriptive and more popular parts of the science; but its higher branches have received some important illustrations. Under the head of Physical Astronomy, there is a general view, by the late Professor Playfair, of the laws which regulate the celestial motions, as discovered by Newton and the philosophers who have succeeded him. Under Attraction, Mr Ivory has given, in a series of distinct propositions, a complete theory, as remarkable for its simplicity and elegance as for its depth, of all that has been discovered relating to the attractions of Elliptical Spheroids. The subject of the Tides, though ably discussed in the Encyclopædia, has been resumed, with great advantage to science, in an article by Dr Young; who has here extended the theory, to the effects of hydraulic resistances of various kinds, which had not been computed by any preceding inquirer.

Electricity and Galvanism also form copious articles in the Encyclopædia; but it was necessary to give a more correct and determinate view of the theoretical parts of both subjects, than is contained in these articles; and also to add such additional facts as have been brought to light by subsequent experiments. This has been done in two supplemental articles, written by M. Biot; of whom it is but justice to mention the alacrity with which his assistance has been given to a work, where his contributions could not appear in the language in which they were written, and to aid which, he could have no other motive but a love for science, and a desire to improve the means of diffusing it in every country of the world.

In passing from the great division of Natural Philosophy, to the other branches of Physical Science, the Editor may state generally, that in these also, the work contains much new and valuable information, contributed by some of their most distinguished cultivators.

With respect to Chemistry, it has the advantage of an instructive historical account of that important science, deduced from the early ages to the close of the last century. This forms one of those Discourses on the History of the Sciences, with which several volumes of the work are prefaced; and it is the only one of the series that has been completed. It was written by Mr Brande, who also contributed a systematic view of the present state of the science; rendered necessary by the 8