PRINCIPIA, the contracted title of the Philosophic Naturalis Principia Mathematica,' the great work of Newton, the publication of which is the most remarkable known epoch in the history of science. The title-page of the first edition is : Naturalis Principia Mathematica. Autore Is. Newton, Trin. Coll. Cantab., Soc. Matheseos Professore Lucasiano, et Societatis Regalia Sodali. Imprimatur. S. Pepys, Reg. Soc. Proses, Jul11 5, 1636. Londini Jussu Societatis Regue ac Typis Josephi Streater. Prostat apud plures Bibliopolas. Anne MDCLXXXVII.' We entirely pass over the common story of the fall of an apple. [Nzwroaa, in Btoo. Div.] It appears in the rough copy left among Newton's papers of the information furnished to Fontenelle for his (loge of Newton : but as Fontenelle did not give it, though very much given to anecdote, it may be inferred that Mrs. Conduitt, Newton's niece, struck it out before it was sent.. It is clear however that New ton first thought on the subject in 1666. With reference to the Story of his laying by the theory until Pieard's measure of the earth was brought to his notice in 1682, it appears that Picard's 316sure do la Terre' was published in 1672, and much discussed at the Royal Society hi the years following.* Moreover Dr. Pemberton, who de rived his information from Newton himself, states most explicitly (in his preface) that a letter from Hooke gave occasion to his resuming his old thoughts, and that he then used Picard's measure. This letter from Hooke, the subject of which was the curve in which a falling body descends to the earth, taking into account the earth's motion, is clearly made out to have been written in 1679, which is therefore the (late of Newton's resumption of his attempt, not 16S2, as generally stated. The new attempt, as every one knows, was more successful, hut Newton did not write any treatise nor contemplate any publica tion ; he traced out the foundation of his system, and threw aside his papers. In January,- 1634, Halley had concluded, from Kepler's third law, that the centripetal force on the planets (supposed to move in circles) was as the inverse square of the distance. Not being able to proceed further, he applied to Hooke and Wren, the former of whom professed to have solved the whole problem, but would communicate nothing ; the latter declared that he had long given over the question from inability to succeed. In August following, Halley paid a visit to Newton at Cambridge, who informed him that he had solved the problem, but was not able to lay his hand on the papers which contained Ills saution, so completely had he thrown the subject aside. After Halley's departure, he worked the theorems out again, and transmitted them to Halley through Mr. Paget, the mathematical master at Christ's Hospital. On receipt of this communication, in November, Halley immediately paid another visit to Cambridge, to gain more informa tion, and to Induce Newton to pursue the inquiry. December 10, 1681, Halley stated at the Royal Society that " he had lately seen Mr.
Newton at Cambridge, and that he had shown him a curious treatise De Motu,' which, upon his desire, lie said was promised to be sent to the Society, to be entered upon their register." Halley and Paget were accordingly deputed to keep Newton in mind of his promise (a singular proceeding, showing how well the Society knew Newton's indifference about. communicating), and the consequence was, that about the middle of February, 1635, a communication (that previously made to Halley, enlarged), entitled Vsa.aci Newtoni Propositiones do Motu,' was sent and registered : it contains what were afterwards the main theorems of the early sections of the Principia, direct and inverse, relating to centripetal forces. No Principia as yet existed, and even this basis bad only recently been written down satisfactorily. Newton writes to Mr. Anton, Sec. ILS., In acknowledging the news of the above entry, " I designed them for you before now, but the examining several things has taken a greater part of my time than I expected, and a great deal of it to no purpose. And now I am to go into Lincolnshire for a month or six weeks. Afterwards I intend to finish it as soon as I can conveniently." ( February 23, 1635.) On this Mr. Itigaud well re marks," The Principia was not a protracted compilation from memo randa which might have been written down under the impression of different trains of thought : it had the incalculable advantage of being composed by one continued effort, during which the mutual bearing of the several parts was vividly present to the author's mind." On the 21st of April, 1680, Halley announced to the Royal Society that Mr. Newton "had an incomparable Treatise on Motion almost ready for the press ; " and on the 28th of the same month Dr. Vincent presented the manuscript of the first book to the Society, who referred the question of printing to the Council, and the production of a report upon the contents to Halley. May 19, the Society decided that the work should be printed forthwith hi quarto, &e.; and hence it has always been supposed that the Society paid the expenses of printing, though the title-page only bears " jussu Soeietatis," &c., and not " jussu et sumptibus," as usual where it bore the expenses. But 3Ir. Rigaud quotes the minute of the Council of the Society of the 2nd of June, confirming the vote of the Society to the extent of resolving "that Mr. Newton's book be pritited," but adding that " E. Halley shall undertake the business of looking after it, and printing it at his owie charge, which he engaged to do." The fact was, that when the Council came to consider the Society's vote of the 19th of May, they found there was no money ; a work of Francis Willtighby, 'De Histeria, Pisciuni,' published " jussu et sumptibus," in 1686, had so reduced their funds, that they were obliged to I:ay their officers in copies of this very book about fishes.