tion. Of these mathematicians, Dr SIMSON, as he may be accounted the last, has also been the most successful, and has left very little room for the ingenuity of future editors to be exercised in, either by amending the text of Euclid, or by improving the translations from it. 1 Such being the merits of Dr Simson's edition, and the reception it has met with having been every way suitable, the work now offered to the public will perhaps appear unnecessary. And indeed, if the geometer just named, had written with a view of accommodating the Elements of Euclid to the present state of the mathematical sciences, it is not likely that any thing new in Elementary Geometry would have been foon attempted. But his design was different: it was his object to restore the writings of Euclid to their original perfection, and to give them to modern Europe as nearly as poffible in the state wherein they made their first appearance in ancient Greece. For this undertaking, nobody could be better qualified than Dr SIMSON; who, to an accurate knowledge of the learned languages, and an indefatigable fpirit of research, added a profound skill in the ancient Geometry, and an admiration of it almost enthufiaftic. Accordingly, he not only restored the text of Euclid wherever it had been corrupted, but in fome cases removed imperfections that probably belonged to the original work; though his extreme partiality paitiality for his author never permitted him to suppose, that such honour could fall to the share either of himself, or of ang other of the moderns. But, after all this was accomplished, something still remained to be done, fince, notwithstanding the acknowledged excellence of Euclid's Elements, it could not be doubted, that some alterations might be made upon them, that would accommodate them better to a state of the mathematical sciences, so much more improved and exe · tended than at the period when they were written. Accordingly, the object of the edition now offered to the public, is not so much to give to the writings of Euclid the form which they originally had, as that which may at present render them most useful. One of the alterations made with this view, respects the Doctrine of Proportion, the method of treating which, as it is laid down in the fifth of Euclid, has great advantages, accompanied with confiderable defects; of which, however, it must be observed, that the advantages are essential to it, and the defects only accidental. To explain the nature of the former, requires a more minute examination than is fuited to this place, which muft, therefore, be reserved for the Notes; and, in the mean time, it may be suf a 3 ficient ficient to remark, that no definition of proportionals, except that of Euclid, has ever been given, from which their properties can be deduced by reasonings, which, at the same time that they are perfectly rigorous, are also simple and direct. As to the defects, the prolixness and obscurity, that have fo often been complained of in this book, they seem to arise entirely from the nature of the language, which being no other than that of ordinary discourse, cannot express, without much tediousness and circumlocution, the relations of mathematical quantities, when taken in their utmost generality, and when no assistance can be received from diagrams. As it is plain, that the concise language of Algebra is directly calculated to remedy this inconvenience, I have endeavoured to introduce it here, in a very simple form however, and without changing the nature of the reasoning, or departing in any thing from the rigour of geometrical demonstration. By this means, the steps of the reasoning which were before far separated, are brought near to one another, and the force of the whole is so clearly and directly perceived, that I am persuaded no more difficulty will be found in understanding the propositions of the fifth Book, than those of any other of the Elements. In the Second Book, also, fome Algebraic figns have been introduced, for the sake of representing more readily the addition and subtraction of of the rectangles on which the demonstrations depend. The use of such symbolical writing, in translating from an original, where no symbols are used, cannot, I think, bę regarded as an unwarrantable liberty; for, if by that means the translation is not made into English, it is made into that universal language so much fought after in all the sciences, but deftined, it would seem, only for the mathematical. The alterations above mentioned are the most material that have been attempted on the books of Euclid. There are, however, a few others, which, though less considerable, it is hoped, may in some degree facilitate the study of the Elements. Such are those made on the definitions in the first Book, and particularly on that of a straight line. А new Axiom is also introduced in the room of the 12th, for the purpose of demonftrating more easily some of the properties of parallel lines. In the third Book, the remarks concerning the angles made by a straight line, and the circumference of a circle, are left out, as tending to perplex one who has advanced no farther than the elements of the science. The 27th, 28th and 29th of the fixth are changed for easier and more simple propofitions, which do not materially differ from them, and which answer exactly the same purpose. Some propofitions also have been added : but, for a fuller detail concerning these changes, 1 a 4 I must refer to the Notes, in which several of the more difficult, or more interesting subjects of Elementary Geometry are treated at considerable length. The SUPPLEMENT now added to the Six Books of Euclid, is arranged differently from what it was in the first edition of these Elements. The First of the three books, into which it is divided, treats of the rectification and quadrature of the circle, subjects that are often omitted altogether in works of this kind. They are omitted, however, as I conceive, without any good reason, because, to measure the length of the simplest of all the curves which Geometry treats of, and the space contained within it, are problems that certainly belong to the elements of the science, especially as they are not more difficult than other propofitions which are usually admitted into them. When I speak of the rectification of the circle, or of measuring the length of the circumference, I must not be supposed to mean, that a straight line is to be made equal to the circum. ference exactly, a problem which, as is well known, Geometry has never been able to resolve : All that is proposed is, to determine two straight lines that shall differ very little from one another, not more, for instance, than the four hundred and ninety-seventh part of the diameter of the circle, and of |