1823.] Prof. Oersted on the Compressibility of Water. 55 



cooling, will partly sink 

 into the capillary tube f, 

 as deep as the mark, g, 

 and separate the water in 

 the flask from that in the 

 outer vessel. This flask 

 is now placed into a strong 

 cylinder of glass A B C D, 

 upon which another smal- 

 lercylinder of brass EFGH 

 is fixed. A piston con- 

 nected with a screw F is 

 moveable in this upper cy- 

 linder. If a pressure by 

 means of this piston be 

 exerted upon the water 

 in the glass cylinder, this 

 will press upon the mer- 

 cury, and thus upon the 

 water in the flask. As 

 soon as the water in the 

 flask is compressed, the 

 mercury in the capillary 

 tube will sink ; and the 

 least pressure produces 

 that effect. To mea- 

 sure the compression, 

 the author fastens the 

 flask in a cylinder of lead 

 d, which bears a scale on 

 which one-fourth part of a 

 French line is marked, and 

 a small glass tube, e f, 

 filled with air, evenly 

 bored, serves to mea- 

 sure the compressing 



power by the compression of the air. All changes of temperature 

 are easily perceived on the narrow neck of the flask much more 

 accurately than on any thermometer ; for an increase of temper- 

 ature amounting to one degree (centigrade) makes the water rise 

 27 lines, its temperature supposed to be about 15°. If the tem- 

 perature is considerably higher or lower, the changes of course 

 will be either greater or smaller. The scale being divided into 

 one-fourth part of a line, and one-eighth being easily perceived 

 by the eye, it is evident that -j-g-g cannot escape observation, 

 and that ^i ? is by no means difficult to observe. It is scarcely 

 necessary to add, that the temperature of the liquid is to be 

 ascertained by a thermometer, at the beginning of the expe- 

 riment. If the experiment be made cmickly, and no per- 



