1823.] Prof. Oersted on the Compressibility of Water. 53 



the better accounted for by the long duration of the heat, or by 

 assuming that this compound, like some others, is more fusible 

 at the moment when its constituents first enter into chemical 

 union. Should it be apprehended that no actual fusion whatso- 

 ever has taken place, the formation and consolidation of the sub- 

 stance by heat without fusion will still furnish the vulcanist 

 with a new point of analogy. 



Believe me, my dear Sir, very truly yours, 



J. J. CoNYBEARE. 



P. S. The character of some portions of this plumbago has 

 struck me as not unlike that ascribed to the points of charcoal 

 altered and fused by voltaic electricity, in some late American 

 experiments. 



Article VII. 



On the Compressibility of Water. By Prof. Oersted.* 



Prof. Oersted, several years since, laid before the Royal 

 Society of Copenhagen some experiments on the compression of 

 water, and showed at that time that this might be effected by a 

 much smaller power than is generally supposed, provided the 

 instrument was constructed according to the well-known prin- 

 ciple, that a pressure acting upon a small surface of an enclosed 

 liquid had the same effect as a power equally great, acting 

 upon each similar part of the whole surface. For the compres- 

 sion of water he made use of a large cylinder of brass upon which 

 one smaller was screwed, furnished with a well-fitted piston. He 

 was, therefore, able to show the compression of water by a small 

 power, quite as well as Abich and Zimmermann haddoneby many 

 hundred pounds weight. To measure the power, a tube full of 

 air, which was confined by mercury, was used, by which contri- 

 vance, of course, the air underwentthe same pressure as the water 

 from which it was separated by the mercury. According to the 

 principle, that the compression of the air is in proportion to the 

 pressing power, it was easy to calculate this power. But notwith- 

 standing the great strength of the brass cylinder in which the water 

 was compressed, it was possible that it might have given way, so 

 that not only the compression of the water might have been mea- 

 sured, but a result obtained, in which the flexibility of the instrument 



* Extracted from a memoir read before the Royal Society of Copenhagen, 1822. 



