FOR PUBLISHING, PERIODICALLY, A COLLECTION OF MATHEMATICAL AND PHILOSOPHICAL TRACTS AND SELECTIONS. THE Utility of a Work of this kind will appear evident in reflecting that a multitude of valuable Tracts, both Mathematical and Philosophical, are interspersed among voluminous collections and expensive publications, and are otherwise inaccessible to the generality of readers. To collect and preserve such Tracts, to compress them into a small compass, and to arrange them in a convenient form, are the objects of the Editors of the Publication which is now offered to the Patronage and Encouragement of the Scientific World. It is not intended to confine the selection to English Works, but occasionally to translate those in other languages which appear to deserve places in this Collection. The Editors propose to publish a Volume annually; or oftener, if it be found necessary and they meet with sufficient encouragement; to contain portions of several valuable tracts, each paged separately, so that, when complete, they may be bound in distinct volumes, or in any manner the purchaser may think proper. A part of each volume will also be reserved for the insertion of shorter extracts and original Communications, which in time will form a valuable miscellaneous volume. Having briefly stated the OUTLINES of their PLAN, the Editors presume to think that the execution of it will be attended with considerable service to the Public and to Science. And in order to render it as perfect as possible, they will thankfully receive any Hints for its Improvement, addressed (Post-paid) to Mr. Glendinning, Bookseller, No. 25, Hatton-Garden, London; Mr. T. Bulmer, Sunderland; Mr. Richard Kay, Aberford, York; Mr. Wm. Wallace, Perth Academy; Mr. John Henry Swale, Chester; Mr. John Lowry, Birimingham; or Mr. N. Bosworth, Peterborough. The First Volume is now in the Press and will soon appear: those Gentlemen who wish to encourage the Work will please to signify their intention, by applying to their respective Booksellers for the Work. PRINTED BY W. GLENDINNING, NO. 25, HATTON-GARDEN. November 1, 1799. This Day is Published. No. VIII. (To be published Half-yearly) PRICE TWO SHILLINGS AND SIX-PENCE, OF THE MATHEMATICAL and PHILOSOPHICAL REPOSITORY: By T. LEYBOURN. CONTENTS OF THIS NUMBER. MATHEMATICS. Atwood's Investigations on Watch Balances Page 125 Demonstrations to several of Stewart's Propositions Page 136 Demonstrations to several of Lawson's Propositions Page 158 A. B. on Fluents Page 160 Three Props. from Lawson, to be demon. in No. X. Page 165 Surtees on Twilight Page 166 Answers to Math. Questions, proposed in No. VI. Page 168 New Questions Page 199 Burrows on Friction Page 204 Dawson on the Distance of the Sun PHILOSOPHY. Dr. Saunderson's Lecture on Optics, concluded Page 246 Gregory on Spring's and Rivers in reply to Kay's letter in Art. 23. Page 254 Solutions to Questions proposed in No. VI. New Questions Crane on Putrefaction Brown on Phosphorescent Bodies LONDON: Printed for the EDITOR; and Sold by Mr. GLEDINNING, Bookseller, Hatton-garden; Mr. O. GREGORY. Bookseller, Cambridge; and Mr. BULMER, Sunderland; of whom may be had any of the former Numbers; or by applying to any of the Booksellers. ADDRESS. The Editor is sorry to be again under the necessity of apologising for the late appearance of his Publication, He is confident, however, of having his apology accepted when he assures his readers that the delay was occasioned by circumstances which he was unable to prevent, and that measures have been taken which it is hoped will ensure the regular appearance of each Number in future. One of these is, a determination to prepare the copy for the press immediately after the limited time is expired, without waiting for any further Communications. While, therefore, the Editor returns his most grateful thanks to his kind contributors for their assistance and support, he begs leave to intreat that they will send their favours early; and he trusts the smallest reflection will convince them of the propriety of the restriction he has adopted. The Editor has not continued Mr. Wallace's Paper on PORISMS, because it is intended for insertion in "A Collection of Mathematical and Philosophical Tracts and Selections"; Proposals for publishing which, accompany this Number. It is intended, in each succeeding Number, to insert accounts of new Mathematical and Philosophical Publications, and short biographical Notices of eminent Mathematicians and Philosophers, recently deceased. Impartial and authentic Communications for these articles will always be thankfully received. The Editor will be much obliged to those Gentlemen who favour him with new questions, as much as possible to compose such as will be of real utility in the various branches, and will generally admit of neat, accurate, and satisfactory answers; he has also to request that such of his correspondents as send him solutions, will be at the trouble to work them throughout, and give the result as well as the method of solution. This would undoubtedly give more satisfaction to the readers of the Repository, and at the same time add to the reputation of its ingenious contributors. The Gentleman who supposes himself alluded to in one of the Replies to Mr. Jogglebelly's Essay on Negroes, would have had his letter inserted, had he not descended to such low and vulgar language as would have disgraced the Repository. It is hoped he will, on reconsidering his letter, acquiesce in this opinion, and that he will also, on further delibration, think the Editor has acted with propriety in not publishing his very violent remarks on an Individual, whom he can assure him, he has, in this case, unjustly accused. To the first of these objections the Letter of L. M. on the same subject, is also liable, and on that account is inadmissible. The Editor wishes by all means to encourage fair and liberal discussion, but he can never consent to make his work the vehicle of scurrility and abuse instead of argument and candour. Librus, of Walton, is informed, in answer to his enquiry concerning Mr. Gregory's "Lessons, Astronomical and Philosophical," that the Editor has not been able to procure him a copy, but he has since heard that a new Edition of that useful performance, enlarged and improved, is just published by Mr. CONDER, No. 30, Buckersbury, London. Mr. Keith's Trigonometry is now in the Press and will soon appear. A Silver Medal will be determined by Lot, as before, among three of the best answerers to each of the Prize Questions. On account of the late appearance of this Number is is proposed to delay the publication of Number IX. until the first of May, 1800, and to extend the time for receiving Communications to the 15th of January. All letters received after that time will positively be too late for insertion in that Number. Number X. will be ready on the first of November, 1800, and all letters intended for its use must come to hand by the 15th of July, or they will be too late. New Editions of Numbers I. and II. will be published speedily. Communications, Post-paid, addressed either to Mr. Glendinning, No. 25, Hatton-Garden; Mr. O. Gregory, Cambridge; Mr. T. Bulmer, Sunderland; or Mr. N. Bosworth, Peterborough, will be thankfully received, and duly forwarded to the Editor. PRINTED BY W. GLENDINNING, NO. 25, HATTON-GARDEN.