54 Prof. Oersted on the Compressibilil r/ of Water. [Jan. 



was included. In the first experiment of M. Oersted, as well as 

 in all those of former philosophers, Canton only excepted, any 

 change of temperature, which might have happened during the 

 experiment, had not been taken into consideration, which, how- 

 ever, in several respects was necessary, as it might even be sup- 

 posed that heat was produced by the very compression. The 

 excellent experiments of Canton, which, in later times, have 

 been almost forgotten, were made with the pressure of condensed 

 and rarified air. But every condensation or expansion of air is 

 accompanied with an adequate elevation or diminution of tem- 

 perature ; it was, therefore, to be feared, that this ingenious phi- 

 losopher had been deceived by this influence. He found the 

 compression of water, at a pressure, equal to that of our atmo- 

 sphere, to be between TTr o 4 4 00 an d twoVoo °^ tne ^ u ^ °^ tlie 

 water. The experiments of Canton possessed a great advantage 

 over all which have recently been made, viz. that the vessel which 

 contains the liquid to be compressed undergoes the same pres- 

 sure both internally and externally ; so that neither its form nor 

 its size can be altered. Within a few years, Mr. Perkins, the 

 ingenious inventor of the siderographia, has made some experi- 

 ments, which have the same advantage as those of Canton ; he 

 included the tube of metal in which the water was to be com- 

 pressed, in water which was exposed to the same pressure. His 

 ingeniously contrived experiments will always be of considerable 

 importance, because he has made them with a power which a 

 philosopher seldom has at his disposal, viz. a pressure several 

 hundred times exceeding that of our atmosphere. It was not, 

 however, his intention to ascertain by these experiments, whether 

 heat was produced by the compression of water, and what 

 influence it had upon the result. Prof. Oersted endeavoured, 

 therefore, to contrive an instrument which allowed an exact 

 measurement of the compressing power, as well as of the com- 

 pression of the water itself, and which at the same time made it 

 easy, exactly to ascertain the influence which heat might have 

 on the effect. The water which is to be compressed is included 

 in a glass tube, a, which holds about two ounces of water : it is 

 closed below, and its upper part terminates in a capillary tube, be, 

 52 French lines long, and of even bore, so that the vessel is like 

 a flask, the neck of which is a long capillary tube. On the 

 upper end of this tube is a small funnel two lines wide. The 

 flask holds 709*48 grammes of mercury, but the mercury which 

 fills 24-6 lines of the capillary tube weighs only 96 milligrammes, 

 which gives To-o-olnroo- for the length of a line, or, to be more 

 exact, O-0000U55O1 of the contents of the flask. When the 

 experiment is to be made, the flask is warmed a little by being 

 kept for a moment in the hand ; if possible the temperature 

 must not rise above ^-° centigrade. Then a drop of mercury is 

 introduced into the funnel, which, while the water in the flask is 



