Davy. I. Sir Hnmphry, an English chemist, born at Penzance, Cornwall, Dec. 17, 1778, died in Geneva, Switzerland, May 29, 1829. He was a healthy, active, and forward child, fond of sports and stories, of retentive memory, and of a remarkably affectionate disposition. Among his boyish tastes was that for fishing, which ho never lost. After a somewhat desultory education, in which he acquired a good knowledge of Latin and Greek, and appears always to have stood at the head of his class, he commenced the study of medicine in February, 1795, under Mr. Borlase, a surgeon and apothecary of Penzance. His attention was naturally turned to chemistry, which he took up with ardor toward the end of 1797, though only as accessory to his medical education. The reading of Lavoisier's "Elements of Chemistry" first led him to the experimental study of the science. His apparatus was of the rudest kind, his materials such as are most commonly used in medicine, and his first experiments were very simple; yet so rapid was his progress that in four months he had sent to Dr. Beddoes a new theory of heat and light, to which the latter became a convert; this was his first publication, which appeared in 1799, in a volume of essays by Dr. Beddoes. Mr. Gregory Watt, a son of the famous James Watt, came to reside at Penzance in the winter of 1797; and in his society, conversation, and sympathy Davy found the stimulus he needed for the development of his intellectual powers.

He also became acquainted with Mr. Davies Gilbert, afterward his successor as president of the royal society of London. The mineralogical and geological structure of the surrounding country, abounding in. tin and copper mines, the lithological character of the cliffs and headlands, and the ever-changing air and sea of that tempestuous climate, invited him to investigate the operation of natural causes; and the undeveloped condition of chemical science was favorable to his rapid advance. His very first original experiments, at the age of 18, were to determine the kind of air which filled the vesicles of the common seaweeds thrown upon the shore, and he demonstrated that the marine plants act upon the air in precisely the same way as the terrestrial, by decomposing carbonic acid under the influence of the sun's rays, to obtain the carbon necessary for their growth, and the oxygen for their respiration. In 1798 he was invited by Dr. Beddoes to become assistant in his pneumatic institution at Clifton, in which pulmonary diseases were treated by the inhalation of different gases; and early in October he went there.

He made his experiments on the protoxide of nitrogen (laughing gas) in 1799, and published the results in 1800; he also experimented with car-buretted hydrogen, carbonic acid, and nitrogen, thereby seriously injuring his health. About the same time he had taken up the subject of galvanism, which afterward led to some of his greatest discoveries in decomposing the alkalies and alkaline earths. The pneumatic institution soon became very popular under his management, and some of the most obstinate diseases were benefited by the new remedies; the nitrous oxide was found very beneficial in many cases of palsy. The royal institution had just been founded, with the intention of diffusing a knowledge of science in its application to the common purposes of life; Davy accepted the invitation to become lecturer on chemistry, took up his abode in London in March, 1801, and was formally appointed professor in May, 1802. His lectures at once became exceedingly popular; his youth, simple manners, and eloquence, his knowledge of his subject, and his brilliant experiments excited the attention of members of the highest ranks in London, and his society was courted by all.

During the 111/2 years that he spent in the rooms of the royal institution, his bachelor apartments were furnished in the simplest manner; in the adjoining laboratory he spent most of his time, preparing for his lectures, and conducting his investigations. His observations on tanning were published in the "Philosophical Transactions" for 1803; and his lectures before the board of agriculture, which were delivered till 1813, were published under the title of "Elements of Agricultural Chemistry," a work which has passed through many editions, and has been translated into almost every European language. His researches in electro-chemical science had been commenced at Clifton, and the results are published in the "Philosophical Transactions" from 1808 to 1812, and in the early "Bakerian Lectures" of 1806-'7. The base potassium was discovered Oct. 6, 1807, and sodium a few days after, by decomposing moistened potash and soda by several voltaic batteries; his delight when he saw the globules of potassium appear and take fire as they entered the air was so great that it was some time before he could compose himself sufficiently to continue the experiment. His mental labor and excitement over his discoveries threw him into a typhoid condition, which threatened his life for several weeks.

On his recovery he experimented with a battery of 2,000 plates, and showed the simple nature of chlorine, sulphur, and phosphorus, and many other important facts. In 1803 he was elected a fellow, and in 1807 one of the secretaries of the royal society, which appoinment he held for five successive years. The medical profession seems now to have been resumed for a short time; but the claims of science had too great an attraction, and he gave up medicine, as he had previously declined an invitation to enter the church. So great was his reputation as a lecturer that he was invited to deliver courses before the Dublin society in 1810 and 1811, for which he received £1,200, and was made doctor of civil law by Trinity college. He was knighted in April, 1812, by the prince regent, and in the same month married Mrs. Apreece, a widow, who brought him a considerable fortune; he was created a baronet in 1818. In the autumn of 1813, by express permission of the French government, granted on account of his scientific reputation, he visited the continent during the war, in company with Mr. Faraday "as his assistant in experiments and in writing." While in Paris, where he spent two months, he became acquainted with Cuvier, Laplace, Gay-Lussac, Humboldt, and Vauque-lin; and during this brief period he discovered that iodine is a simple substance, analogous in its chemical relations to chlorine.

He remained on the continent until the spring of 1815, visiting the south of France, Italy, and Switzerland, devoting special attention to the volcanic regions, and pursuing his chemical researches on colors, the iodine compounds, and oxymuriate salts, which were published in the "Philosophical Transactions" for 1815. His next discovery placed him among the greatest benefactors of his race. In May, 1812, a terrific explosion of gas took place in the Felling colliery near Newcastle, causing the death of 92 men; and after many other such disasters^ a committee of proprietors of mines waited upon Davy to see if he could devise any way of preventing similar accidents. He began by analyzing the gas, and ascertaining in what proportions its mixture with air rendered it most explosive, and the degree of heat necessary to ignite it; from observing that the combustion was not communicated through tubes of small dimensions, he gradually reduced the length of the tubes till he found that a simple metallic gauze, with apertures not exceeding 1/22 of an inch square, was sufficient to prevent the burning gas inside from igniting the great explosive mass on the outside; he accordingly covered the lamps with a wire tissue, permeable to air and light, but not to flame.

This simple contrivance constituted the miner's safety lamp, and has saved the lives of thousands; the dangerous gas may burn within the gauze, and thus give timely warning, and may at last extinguish the lamp, but a suspended platina spiral will remain glowing in the midst of the explosive gas, and enable the miner to see as long as the air is fit for respiration. His attention was first drawn to the subject in August, 1815, and in December his lamp was completed. Urged to take out a patent for his invention, he replied: "No, my good friend, I never thought of such a thing; my sole object was to serve the cause of humanity; and if I have succeeded, I am amply rewarded in the gratifying reflection of having done so." At the same time George Stephenson was engaged in a similar investigation, and invented a safety lamp embodying essentially the same principles as that of Davy. The two inventions appear to have been made almost simultaneously, each independently of the other. The priority was, however, awarded to Davy, to whom the mining proprietors in 1817 presented a service of plate valued at £2,000, awarding £100 to Stephenson, who was then a mere mining operative.

A sharp controversy sprang up, and a further sum of £1,000 was raised and presented to Stephenson. The service of plate presented to Davy was bequeathed by his widow, who died in 18C8, to the royal society, to be sold, and the proceeds applied to the encouragement of science. In May, 1818, Davy set out on a second continental journey, visiting Germany, Hungary, and Italy, and returning to England in June, 1819. On the death of Sir Joseph Banks in 1820, he was elected president of the royal society of London, and was annually reelected for seven years. The last term of his scientific labors extends from 1823 to the summer of 1826, during which time he communicated to the royal society three papers on the preservation of metals by electro-chemical means, and the Bakerian lecture for 1826, "On the Relation of Electrical and Chemical Changes." As in the case of the safety lamps, these papers were intended to remedy a practical evil. His attention was directed by the commissioners of the navy to the corrosion of the copper sheathing of vessels by sea water; he ascertained that the popular notion that impure copper is soonest corroded was an error, and that the corrosion is owing to the joint action of the air and the saline ingredients in the water; he succeeded in preserving the copper sheathing from corrosion by rendering it negatively electrical by small pieces of tin or zinc, or iron nails, these metals making a surface of copper from 200 to 300 times their own size so electrical as to have no action on sea water.

The very perfection of the protection rendered this method practically inapplicable, as shells and seaweeds adhered to the non-corroded surface; but this principle of galvanic protection has been successfully applied to various important uses in the arts and sciences. In 1824 he made a journey to Norway, Sweden, Denmark, Hol-stein, and Hanover, fishing and hunting, and communicating with their eminent men, among whom were Berzelius, Oersted, Gauss, Olbers, and Schumacher. In 1825 he began to experience considerable indisposition, which ever after affected his ordinary elasticity of spirits, depressed also by the illness and death of his mother in 1826. He had suffered for more than a year with numbness and pain in his right arm, when toward the close of 1826 a paralytic attack affected his right side; his mental faculties were not impaired, and while confined to his room he corrected the proof sheets of his "Discourses to the Royal Society," published in January, 1827. In this month he had so far re-. covered as to start on a journey to the continent, going through France over Mont Cenis into Italy, where he occupied himself in hunting, fishing, and observations on natural history and chemical science, for about three months; he then journeyed through various parts of southern Germany and Switzerland, returning in October, with health and strength slightly improved, to England, where he remained until March, 1828. " Salmonia, or Days of Fly Fishing," is a kind of dramatization of the most interesting parts of his journal in these last travels, rendered doubly valuable by his observations in natural history.

Finding no permanent improvement in his health, he left London again in March, 1828, for the Alpine regions of southern Austria, where he passed the summer, spending the winter in Italy; during this journey he wrote " Consolations in Travel," his last writing, which Cuvier calls the work of a dying Plato. On Feb. 20, 1829, he experienced at Rome a sudden and severe paralytic attack, which ultimately proved fatal, though he so far improved as to quit Rome on the last of April for Geneva, where he arrived May 28. At 2 1/2 the following morning he was taken alarmingly ill, and in a few moments expired; he was buried, in accord- • ance with his expressed wish, where he died, in the city of Geneva, on June 1. His brother believed that the paralysis was caused by softening of the brain, which, with some enlargement of the heart, was the cause of his death. Sir Humphry Davy was of middle stature, 5 ft. 7 in. in height, well proportioned and muscular, and able to endure considerable fatigue; of sanguine temperament, warm in his feelings, of cheerful disposition, fond of company, persevering and observing.

He was chosen a member of the French institute in 1817; he was also connected with most of the great academies of Europe, and was by universal consent considered without a superior, if he had an equal, among the chemists of his time. His memory is cherished at Geneva, where his widow founded a prize in his honor, to be given every two years for the most original and important discovery in chemical science. . A statue, after the portrait by Lawrence, is to be erected to his memory at Penzance, at a cost of £6,000. Besides the life by his brother, there is one by John Ayrton Paris, M. D. (2 vols. 8vo, London, 1831). II. John, an English physician, brother of the preceding, born at Penzance, May 24, 1791, died April 24, 1868. After taking his degree of M. D. at the university of Edinburgh in 1814, he was attached to the English army, and travelled extensively in the East. He was the author of several works, the principal of which are: " Life and Works of Sir Humphry Davy " (9 vols., London, 1839-40, the life constituting vol. i.); "An Account of the Interior of Ceylon and of its Inhabitants, with Travels in that Island" (4to, London, 1821), especially valuable for its details on the natural history of Ceylon; " Researches, Physiological and Anatomical" (2 vols. 8vo, London, 1839); "Notes and Observations on the Ionian Islands and Malta, with some Remarks on Constantinople and Turkey" (2 vols. 8vo, 1842); and "Diseases of the Army " (1863). He spent most of his life in the foreign army service, but was the travelling companion and physician of his illustrious brother during the last period of his life.

He published many important papers in the "Philosophical Transactions," several of which are collected with illustrations in his "Researches." In 1858 he published "The Fragmentary Remains of Sir Humphry Davy".