56 Prof. Oersted on the Compressibility of Water. [Jan 



sons present beside the observer, the difference in the height 

 of the mercury before and after the experiment will generally 3 

 one-eighth of a line ; frequently, however, one-fourth. In the 

 first case, it announces a change of temperature amounting to 

 not quite -g^U- , in the second to hardly -^^°. If the expe- 

 riment be performed slowly, the difference may be one-half, and 

 even one line. In every case the mean height between these 

 two observations is to be taken. By a long series of experiments, 

 of which the most accurate were made at a temperature of 15 — 16*, 

 a pressure equal to one atmosphere has produced a com- 

 pression = 0-000047 of the original bulk of the compressed 

 water. Several alterations on the pressure, from one-third to 

 five atmospheres, were tried, and agreed in proving, that the 

 compression is in direct proportion to the compressing power. 

 The same result had been deduced by the author from his 

 former experiments, which, however, were influenced by the 

 giving way of the metallic vessel ; the expansion of which must 

 likewise be in proportion to the pressing power. 



It seems pretty evident that no heat is produced by this con- 

 densation of the water, the limit between mercury and water 

 being, after the experiment, on the same place as before ; the 

 insignificant elevation of temperature must be considered as a 

 necessary result of the contact of the observer during the 

 experiment. Even after a pressure of five atmospheres, the 

 difference of temperature was not quite - r ^ s -°, and in general 

 neither greater nor less than that, if only a pressure of one atmo- 

 sphere had been used. It was, however, possible, that the expan- 

 sion of the water when the pressure had ceased, would absorb 

 the heat produced before by the compression; therefore a 

 thermometer of Breguet, on which a difference of -^th of a 

 degree may easily be perceived, was placed in the water in the 

 large cylinder, and exposed to the greatest compression which 

 could be procured, but not the least trace of any change in the 

 temperature was observable. The manner in which these expe- 

 riments of Prof. Oersted agree with those of Canton is really 

 interesting. The English philosopher had at 64° Fahr. = 15^° 

 centigrade, a compression of 100 V eoo b Y n pressure ec l ual to one 

 atmosphere, and at 34° Fahr. = 1 T V° centigrade, it was ifraVWb ' 

 This rather unexpected result may easily be explained by small 

 differences in the temperature, but it does not, on either side, 

 deviate much from the result Prof. Oersted obtained, which was 



4 7_ 



"l"o O U U ' 



