12 Memoir of M. D' Aubuisson de Voisins. 



means of mining pits, which consists in building a tower of 

 masonry on the surface of the ground, which is allowed to 

 sink by its own weight. This process, so original in its in- 

 vention, had been brought into Silesia by a Frenchman, and 

 has been since employed with much success, again by a 

 Frenchman, in piercing one of the most beautiful subter- 

 ranean works in existence, the tunnel under the Thames. 



Also in 1806, M. D'Aubuisson wrote a first memoir on the 

 measurement of heights by the barometer, the formula of 

 which he discussed and modified ; thus forming a prelude to 

 his more impoi'tant barometrical works, of which we shall 

 speak afterwards. He employed another portion of the same 

 year in expei'imenting on the useful effects of the hydraulic 

 machines of Poullaouen and Huelgoat, in Bretagne, and on 

 the temperature in the interior of mines, in continuation of 

 studies of the same kind undertaken at Freiberg. We ought 

 likewise to mention some chemical investigations which 

 occupied him during this period of his studious life, parti- 

 cularly researches on the hydrate of iron, by which he shews 

 that the water in it is combined with oxide of iron in defi- 

 nite proportion, a circumstance which was not at that time 

 without novelty. 



We now reach the period when M. D'Aubuisson obtained 

 that reward of his labours of which he was most ambitious, 

 because it enabled him to employ the future in satisfying his 

 tastes, and in prosecuting the object of his long continued 

 study ; on the 13th February 1807, he was attached to the 

 Corps des Mines, with the title of engineer. The following 

 was the occasion of this appointment. The French territory 

 having become greatly extended, by conquest, the Emperor 

 wished that four engineers should be appointed to the new de- 

 partments which had been formed at the expense of Piedmont, 

 Belgium, and Switzerland. The members of the engineering 

 department were limited in number, and two eleves only were 

 disposable; althDugh it was the rule that it could be aug- 

 mented only by drawing from the Ecole Poly technique, yet 

 the need of men of knowledge and experience being imme- 

 diate, M. D'Aubuisson was proposed by the Council of 

 Mines, and soon after nominated. The service of the de- 



