PREFACE.

It seems necessary to explain in few words the circumstances which induced me to undertake the difficult task of becoming Dalton's biographer, and which have so long delayed its accomplishment.

Dr. Dalton, in the first clause of his will, bequeathed to me and to his three executors "all his philosophical, scientific, and literary manuscripts and correspondence, to be disposed of as they may judge most fit;" and in a codicil to the same, he bequeathed to me all his chemical and other philosophical instruments and apparatus. I received intelligence of these bequests in August 1844, at Paris, on my way to Italy, where I remained till the following autumn. Regarding them as significant of my venerable friend's intention that I should act as his literary executor, and should write some account of his life and discoveries, I commenced shortly after my return to prepare for the task, by the careful re-perusal and analysis of all his published works. I also applied to Mr. Peter Clare, the acting executor, into whose hands the manuscript remains of Dalton had fallen, for those

documents. Mr. Clare, who had for many years stood in most intimate relations with Dr. Dalton, and placed the highest value on the papers in his possession, manifested on the numerous occasions when I applied for them, personally and by letter, great reluctance to resign them to me. On one occasion he proposed a joint authorship of Dalton's life, which I declined. He finally promised to bring the documents to me in the country, on the ground that they needed his oral comments; a promise he was never able to fulfil. After his decease they were forwarded to me by the surviving executor, Mr. Neild, to whom I am also indebted for promptly and courteously imparting to me all further information to which he had access. Early last spring, shortly after I had received the manuscripts, and indeed before I had been able to inspect them, Mr. Graham did me the honour to invite me, on the part of the Cavendish Society, to write a Life of Dalton for their volumes. This flattering invitation determined me at once to undertake the task.

The MSS. remains of Dalton consist of his early scientific journals, chiefly devoted to meteorology; of note-books, containing records of short excursions in England and Wales; of a correspondence which he had maintained with his brother, Jonathan Dalton, a schoolmaster at Kendal, between the years 17931824; of a few letters from men eminent in science;

1836-42,

and of a letter-book, into which he had copied all important letters written by him in the years Of these documents the letters addressed to his brother throw most light on his scientific researches and habits of life. I have applied to all scientific persons, likely to be in correspondence with Dalton, for his letters, but with only limited success. Mr. Jonathan Otley, of Keswick, a few months Dalton's senior, and still surviving him, has contributed several letters and an interesting narrative of their joint mountain excursions in the Lake District. I have been favoured by Mr. I. F. Crosthwaite with a valuable series of letters, addressed to his grandfather, Mr. Peter Crosthwaite of Keswick, relating chiefly to meteorological observations. I am also indebted to Mr. Giles, Mr. Woolley, and Mr. Wilkinson, for permission to peruse and extract from biographical notices of Dalton, read by them before the Literary and Philosophical Society of Manchester, and still unpublished. Mr. Woolley has also most obligingly placed at my disposal the sketch of Dalton's domestic habits by the late Miss Johns, in whose father's house Dalton was an inmate during a considerable part of his life. Dr. Davy, besides permitting me to publish inedited notices of Dalton by his brother, Sir Humphry Davy, and by himself, has with the greatest kindness procured for me

many interesting particulars respecting Dalton's early life, as a schoolmaster, in Kendal. Among my father's papers also I discovered many valuable documents; as notes of conversations with Dalton, and several letters from Mr. G. W. Wood, Mr. Babbage, and other persons respecting Dalton's pension. These materials had been collected and preserved by my father with a view of their being made available for a future biography of Dalton, a work which he was desirous that I should undertake. My friend Mr. Joseph A. Ransome has favoured me with a narrative of Dalton's illness and death, and with an interesting letter, detailing his own reminiscences of Dalton.

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The only published notices of Dalton which I have consulted are those by Dr. Thomson, in his History of Chemistry, and in the Proceedings of the Glasgow Philosophical Society; that by Dr. Hermann Kopp a short account of his life, said to have been corrected by himself, which appeared in Wheeler's History of Manchester; and especially an elaborate and well-conceived article in the British Quarterly Review, vol. i., by Dr. G. Wilson, the accomplished biographer of Cavendish,-beyond comparison the ablest and justest appreciation that has yet appeared of Dalton's philosophical character and discoveries. To Dr. G. Wilson I am also indebted for

*Geschichte der Chemie, theil i. p. 362.

the frank and liberal communication of his views respecting colour-blindness, and of all sources of information known to him respecting Dalton.

Dr. Dalton's life was marked by few external events. Its main incidents were mental efforts, resulting in signal discoveries. To accomplish the clear enunciation of these, which constitute the staple material of his biography, I have been compelled to depart from a strictly chronological order. For Dalton, it will be seen, grappled in early years with several fundamental problems in the philosophy of heat and meteorology, and carried about with him these favourite speculations, bound up in his inmost nature, during a long life; attracted to them again and again, either by the workings of his own thoughts or by the critical notice of his contemporaries. Though averse to change, he often materially modified his original conceptions. In order, therefore, to avoid the confusion of constant recurrence to the same questions, I have deemed it expedient on the first appearance of each of his master ideas, excepting the Atomic Theory, to trace its subsequent development and to exhaust the subject before breaking fresh ground. I have also endeavoured, as far as consisted with my own limited knowledge, to supply the corrections or confirmations, which the ideas and experimental results of Dalton have subsequently received, and to define