No. XXI. DEDICATION AND PREFACE TO "THE HISTORY OF THE PRESENT STATE OF DISCOVERIES RELATING TO VISION, LIGHT, AND COLOURS." London, 1772.* DEDICATION. To His Grace the DUKE OF NORTHUMBERLAND, Earl Percy,t &c., &c., &c. MY LORD, It is with peculiar satisfaction that I dedicate the first volume of so extensive a work as that of The History of all the Branches of Experimental Philosophy, to a nobleman of your Grace's known attachment to the sciences, and one who has, on so many occasions, distinguished himself by his generous patronage of them. It is for the honour of any country, and of any age, in which persons of your rank and fortune choose to appear in that character. No branch of science stands in so much need of the aid of the Great as that which is the subject of this work. But, on the other hand, from no branch of science do they derive greater advantage; for, without that knowledge about which it is conversant, rank and fortune would be of little value, the elegant enjoyments of life being derived from no other source than those arts which owe their birth to our acquaintance with the powers of nature. By this species of knowledge it is that mankind in general are capable of improving their situation in the world, making the most of every advantage it affords, and obviating the inconveniences to which it is liable. These studies, also, having the works of God for their object, are of eminent use to extend the views and enlarge the comprehension of the human mind, by which means the dignity of our nature is increased, and the best foundation is laid for our advancement in intellectual happiness. As the English philosophers have particularly distinguished themselves by their improvements in natural knowledge, your Grace, who, in a variety of capacities, so eminently supports the dignity of the English nation, acts peculiarly in character by your patronage of that branch of philosophy for which your country has long been famous. That your Grace may long enjoy the exalted satisfaction of promoting a science so truly worthy of your taste, is the sincere prayer of, My Lord, Your Grace's most humble and most obliged servant, * The motto, Facta est immensi copia mundi. OVID. See Vol. I. Mem. 104. + To whom Dr. Priestley had been introduced by Mr. Lindsey, who, in 1751, &c., had attended the Duke, when Lord Warkworth, during a residence in France. VOL. XXV. 2 L Preface. In order to facilitate the advancement of all the branches of useful science, two things seem to be principally requisite. The first is, an historal account of their rise, progress, and present state; and the second, an easy channel of communication for all new discoveries. Without the former of these helps, a person every way qualified for extending the bounds of science labours under great disadvantages, wanting the lights which have been struck out by others, and perpetually running the risk of losing his labour, which is a great mortification and discouragement. In other respects also, the progress of natural knowledge is retarded on this account, so that in the present state of science such histories as these are, in a manner, absolutely necessary." Considering how very few persons are acquainted with the present bounds of any branch of science, or indeed are in circumstances in which it is possible for them to acquire that knowledge, and how much time and labour are even in that case necessary in order to acquire it, it must be allowed that, were those histories judiciously compiled, real discoveries would be much more numerous; and were these, again, easily and expeditiously circulated, the progress of knowledge might be accelerated beyond what we can now conceive. At present, philosophical knowledge is so dispersed in various books and languages, that the very reading of what is absolutely necessary, in order to be properly acquainted with any one branch of it, would take up more time and attention than any person, though ever so much devoted to philosophical pursuits, would ever think of bestowing upon it, unless he should make it his business to digest the materials into a history or system for the use of others as well as of himself; not to mention the expense of purchasing the books that he would want, which would be several hundred pounds for any one branch of the science; since for this purpose he must at least be possessed of the periodical publications of all the philosophical societies of note in Europe. Having had my mind strongly impressed with the idea of the great importance of full and complete histories of the several branches of experimental philosophy, from my own experience of the want of them, ever since I gave any attention to the subject, I ventured upon a plan of this kind for one of the branches to which at that time I happened to be more particularly attached, viz. Electricity; and though I had very great difficulties to struggle with in the execution of it, particularly from the want of a sufficient stock of materials when I first began to compose, I had so many other advantages, especially those which I derived from my intimacy with the persons who were most distinguished for their improvements in that branch of science, that I believe the work is held in some degree of esteem by the judicious and the candid. This success has encouraged me to endeavour to carry my original design to its just extent, and to attempt the history of all the remaining branches of experimental philosophy. It will be seen, in the preface to the first edition of the History of Electricity,* that I then considered the history of all the branches of experimental philosophy as too great an undertaking for any one person; but, like the fox with respect to the lion, a nearer view has familiarized it to me, and I now look upon it not only without dread, but with a great deal of pleasure, considering it not only as a very practicable business, but even as an agreeable amusement. I am satisfied that it is not to be compared to many works which have been executed by single persons, of moderate abilities, but pretty close application, and who have not been possessed of more zeal and good-will to their undertakings than I have for this. A very great degree of enthusiasm would not answer the purpose. That could only carry a man through some single and great effort; whereas the thing that is wanted is a moderate and constant attention for a course of some years. Such an attention, however, can hardly be expected to be kept up by a mere writer, compiler, and historian. It is in a manner necessary for this purpose that a man have such a taste for experimental philosophy as will engage him in similar pursuits. This will give him a clearer idea of the business about which he writes. In short, he will have the same advantage in a work of this kind that Xenophon, Cæsar, and other warriors, are allowed to have had in describing a battle, and which eminent statesmen, well versed in public affairs, have had in writing general history. I hardly need to observe, however, that a mere philosopher is as little qualified for this undertaking as a mere writer. To execute a work of this extensive kind to advantage, a person must have acquired such a skill in selecting, abridging, and managing the materials that come before him, and such a readiness in composition, as, like other arts and habits, can only be acquired by much practice. me. The pleasure I have in this undertaking is not so great but that it will depend upon the reception my labours meet with, whether I continue them or not. If those persons for whose opinion I have an esteem favour me with their approbation, and the sale of the work indemnify me for the very great expenses I have been at on account of it, I shall persevere with pleasure. If the reception be unfavourable in these respects, I shall certainly desist, and be thankful that I can betake myself to other studies not less agreeable to As to the opinion of those for whom I have no esteem, on account of the unworthy motives by which their judgments are influenced, they will not weigh with me at all. A man must have had little experience of life, and have acquired very little strength of mind indeed, to be diverted from an undertaking which he believes to be useful and important to mankind, on account of trifling, unjust, or unreasonable censure. It cannot be expected, however, but that a work of this extensive kind, though it were undertaken by ever so many persons, even the ablest, and, in all respects, the most proper for the purpose, should be free from imperfections and errors; and the uniformity, and other advantages, which must result from its being executed by a single person, will, it is hoped, * Supra, pp. 344, 345, 348, 349. be a sufficient plea for the greater indulgence which he will necessarily stand in need of. Some will probably think that it would have been more advisable for a person who meant to do the whole of this work, to have undertaken to do no more than one branch of the science at one time, and not to have done any thing with respect to another till that had been finished. But, besides that the expense of executing any one part completely is not much less than the whole will require, two other capital advantages attend the undertaking of the whole at once; for by this means there is no occasion for any philosophical treatise to go through the writer's hands more than once in order to common-place all the materials it contains; and then, having his whole subject in view, nothing that is to his purpose can well escape his notice'; whereas, upon the other plan, he would be under the necessity of examining a great number of volumes many times over; and, never having more than one single object in view, articles lodged in unsuspected places would entirely escape him. Indeed, let a man use all the precautions he can possibly think of, he must expect to overlook some things, even though he had access to all the books that he wanted, unless he should actually compose the whole before any one part went to the press, which is much too hazardous for any person to think of. The reason of this is, that the titles of books and papers are no sufficient indication of their contents, on account of their often being very miscellaneous, or ill arranged; and if a person actually read every page of an author, he may almost as well write a full account of it for the use of his work. I would not have my reader imagine that this work, though written by a single person, contains nothing more than his own observations, which might well be concluded to be very inadequate to the purpose. I have not the vanity to pretend to an universal knowledge of philosophy; indeed, no man can pretend to it; but I am happy in my friendships with those who are allowed to be the most eminent in each of the branches, and no part of the work will be put to the press till it has received the benefit of all the assistance that they can afford with respect to it; and none of them will say that I am not very thankful for any information they give me, and very ready to correct the mistakes that I fall into. With respect to the present volume, the reader will easily perceive that both he and I are obliged to my friend and neighbour, the Rev. Mr. Mitchell,* for many original communications, and my obligations to him are much more considerable than will appear on the face of the work. Indeed, several of the observations will be seen to have the marks of a more accurate acquaintance with the subject than I can pretend to. With respect to several articles, however, I was so circumstanced as to be under a necessity of sending them to the press without consulting either Mr. Mitchell or any other person whatever, so that if any mistake be discovered in the work, myself only am answerable for it. Sensible how inadequate the information and furniture of any * See Vol. I. Mem. 105. single person must necessarily be for a work of this extent, I have made use of every precaution that my prudence could point out to me to remedy that defect. I began with publishing printed proposals for the undertaking, with lists of the books I had procured, and also of those which I had heard of, and which I wanted for the purpose. This method having answered my design, I repeated my address to the public with new and larger catalogues; and now I think it unnecessary to do it any more, imagining that I am possessed of all the philosophical writings that can be of much use to my design. Lest, however, I should have overlooked any work of value, I shall at the close of this, and also of every other volume, print a catalogue of all the philosophical books that I have access to, that those persons who have it in their power may have an opportunity of giving me the information or assistance that I still may want, and for which I shall be very thankful. I have adopted the historical method, because it appears to me to have many obvious advantages over any other for my purpose, being peculiarly calculated to engage the attention, and to communicate knowledge with the greatest ease, certainty, and pleasure. Moreover, the recital of the labours of philosophers in an historical method gives a writer a better opportunity than a systematical method would do of transmitting them to posterity, in such a manner as will operate most powerfully on the minds of the readers, and be a motive with them to exert and distinguish themselves in philosophical pursuits. To such considerations as these the mind of man is never wholly insensible. It will, however, be found, that though the method I have chosen be historical, it is at the same time sufficiently systematical, and indeed pretty strictly so with respect to each distinct article in the several periods into which the work is divided; so that any person, if he choose it, may see without interruption all the discoveries that have been made relating to any single head or division of every subject. In order to be more systematical, and thereby to make the work more useful to young students, I have imitated the conduct of the best civil historians, in making the order of time give place, with respect to many articles, to more natural, and therefore more important connexions. Thus when later writers have added but little to the observations of those who preceded them, I have given the whole of a subject in an earlier period; and when former writers contain very little, I have given the whole in a later period. This method cannot but be more agreeable to all my readers than a mere journal, or a strictly chronological narrative of trans actions. That the generality of readers may not be discouraged from purchasing this work, I shall endeavour to make every thing, at least every thing of much value in it, perfectly intelligible to those who have little or no knowledge of mathematics, provided they give a proper degree of attention to the subject. I shall also endeavour to avail myself of every circumstance or incident that can contribute to render the narration pleasing and interesting to the reader, at the same time that I shall be careful never to lose sight of my principal object, which is to bring into a moderate compass, |