In 1745 he was named to go to Lyons in order to examine with care the processes followed for refining gold and silver. Before his return he took care to give to these processes the requisite precision and exactness. Immediately after his return to Paris he was appointed to examine the different mines and assay the different ores in France; this appointment led him to turn his thoughts to the subject. The result of this was the publication of an excellent work on assaying and metallurgy, entitled “De la Fonte des Mines, des Fonderies, &c. Traduit de l’Allemand de Christophe-André Schlutter.” The first volume of this book appeared in 1750, and the second in 1753. Though this book is called by Hellot a translation, it contains in fact a great deal of original matter; the arrangement is quite altered; many processes not noticed by Schlutter are given, and many essential articles are introduced, which had been totally omitted in the original work. He begins with an introduction, in which he gives a short sketch of all the mines existing in every part of France, together with some notice of the present state of each. The first volume treats entirely of docimasy, or the art of assaying the different metallic ores. Though this art has been much improved since Hellot’s time, yet the processes given in this volume are not without their value. The second volume treats of the various metallurgic processes followed in order to extract metals from their ores. This volume is furnished with no fewer than fifty-five plates, in which all the various furnaces, &c. used in these processes are exhibited to the eye.
While occupied in preparing this work for the press he was chosen to endeavour to bring the porcelain manufactory at Sevre to a greater state of perfection than it had yet reached. In this he was successful. He even discovered various new colours proper for painting upon porcelain; which contributed to give to this manufactory the celebrity which it acquired.
In the year 1763 a phenomenon at that time quite new to France took place in the coal-mine of Briançon. A quantity of carburetted hydrogen gas had collected in the bottom of the mine, and being kindled by the lights employed by the miners, it exploded with great violence, and killed or wounded every person in the mine. This destructive gas, distinguished in this country by the name of fire-damp, had been long known in Great Britain and in the Low Countries, though it had not before been known in France. The Duke de Choiseul, informed of this event, had recourse to the academy for assistance, who appointed Messrs. de Montigny, Duhamel, and Hellot, a committee to endeavour to discover the remedies proper to prevent any such accident from happening for the future. The report of these gentlemen was published in the Memoirs of the Academy;[182] they give an account both of the fire-damp, and choke-damp, or carbonic acid gas, which sometimes also makes its appearance in coal-mines. They very justly observe that the proper way to obviate the inconveniency of these gases is to ventilate the mine properly; and they give various methods by which this ventilation may be promoted by means of fires lighted at the bottom of the shaft, &c.
In 1763 M. Hellot was appointed, conjointly with M. Tillet, to examine the process followed for assaying gold and silver. They showed that the cupels always retained a small portion of the silver assayed, and that this loss, ascribed to the presence of a foreign metal, made the purity of the silver be always reckoned under the truth, which occasioned a loss to the proprietor.
His health continued tolerably good till he reached his eightieth year: he was then struck with palsy, but partially recovered from the first attack; but a second attack, on the 13th of February, 1765, refused to yield to every medical treatment, and he died on the 15th of that month, at an age a little beyond eighty.
Henry Louis Duhamel du Monceau was born at Paris in the year 1700. He was descended from Loth Duhamel, a Dutch gentleman, who came to France in the suite of the infamous Duke of Burgundy, about the year 1400. Young Duhamel was educated in the College of Harcourt; but the course of study did not suit his taste. He left it with only one fact engraven on his memory—that men, by observing nature, had created a science called physics; and he resolved to profit by his freedom from restraint and turn the whole of his attention to that subject. He lodged near the Jardin du Roi, where alone, at that time, physics were attended to in Paris. Dufoy, Geoffroy, Lemery, Jussieu, and Vaillant, were the friends with whom he associated on coming to Paris. His industry was stimulated solely by a love of study, and by the pleasure which he derived from the increase of knowledge; love of fame does not appear to have entered into his account.
In the year 1718 saffron, which is much cultivated in that part of France formerly distinguished by the name of Gâtinois, where Duhamel’s property lay, was attacked by a malady which appeared contagious. Healthy bulbs, when placed in the neighbourhood of those that were diseased, soon became affected with the same malady. Government consulted the academy on the subject; and this learned body thought they could not do better than request M. Duhamel to investigate the cause of the disease; though he was only eighteen years of age, and not even a member of the academy. He ascertained that the malady was owing to a parasitical plant, which attached itself to the bulb of the saffron, and drew nourishment from it. This plant extended under the earth, from one bulb to another, and thus infected the whole saffron plantations.
M. Duhamel formed the resolution at the commencement of his scientific career to devote himself to public utility, and to prosecute those subjects which were likely to contribute most effectually to the comfort of the lower ranks of men. Much of his time was spent in endeavouring to promote the culture of vegetables, and in rendering that culture more useful to society. This naturally led to a careful study of the physiology of trees. The fruit of this study he gave to the world in the year 1758, when his Physique des Arbres was published. This constitutes one of the most important works on the subject which has ever appeared. It contains a great number of new and original facts; and contributed very much indeed to advance this difficult, but most important branch of science: nor is it less remarkable for modesty than for value. The facts gathered from other sources, even those which make against his own opinions, are most carefully and accurately stated: the experiments that preceded his are repeated and verified with much care; and the reader is left to discover the new facts and new views of the author, without any attempt on his part to claim them as his own.
M. Duhamel had been attached to the department of the marine by M. de Maurepas, who had given him the title of inspector-general. This led him to turn his attention to naval science in general. The construction of vessels, the weaving of sailcloths, the construction of ropes and cables, the method of preserving the wood, occupied his attention successively, and gave birth to several treatises, which, like all his works, contain immense collections of facts and experiments. He endeavours always to discover which is the best practice, to reduce it to fixed rules, and to support it by philosophical principles; but abstains from all theory when it can be supported only by hypothesis.
From the year 1740, when he became an academician, till his death in 1781, he made a regular set of meteorological observations at Pithiviers, with details relative to the direction of the needle, to agriculture, to the medical constitution of the year, and to the time of nest-building, and of the passage of birds.