1880.] Lowering of the Freezing-Point of Water by Pressure. 533 



hence it cannot have altered more than 23 vibration, for which, 

 the rnst fully accounts. At the same time five other forks, of a large 

 size and very different make, after having journeyed to America and 

 back to be measured by Professor Mayer, have, according to Professor 

 McLeod's measures, lost -0015, -165, '0205, '0285, and "014 vibration 

 respectively. The second fork was not so good as the rest, and may 

 possibly have been slightly wrenched, as it had to be screwed in and 

 out of a wooden holder. The other losses scarcely exceed errors of 

 observation and differences of estimation of the effects of temperature. 



The points to which I wish to draw attention are, the establishment 

 of the acceleration of beats which take place in confined spaces, and 

 the corroboration of Helmholtz's theory of the objective existence of 

 partial tones, by means of beats of these partial tones, either with one 

 another or with those of other compound tones. 



II. " On the Lowering of the Freezing-Point of Water by Pres- 

 sure." By James Dewar, M.A., F.R.S., Jacksonian Pro- 

 fessor of Natural Experimental Philosophy in the University 

 of Cambridge. Received June 10, 1880. 



The Cailletet pump may be conveniently employed to observe the 

 thermal effects of compression on solid and fluid substances. Before 

 engaging in an investigation on this subject, it was necessary to test 

 the apparatus, and especially the manometer. For this purpose it 

 seemed, on theoretical grounds, that observations on the lowering of 

 the freezing-point of water by pressure would be a severe test of the 

 accuracy of the pressure gauge, and the constancy of the records of the 

 thermo- junctions under pressure. I am not aware of any quantitative 

 experiments on this subject having been made under high pressures. 

 Sir William Thomson carried the proof of the accuracy of Professor 

 James Thomson's great theoretical discovery to a pressure of 17 at- 

 mospheres.* The experiments of Mousson (" Pogg. Annalen," 1858) 

 were not of a quantitative character, being merely intended to show 

 that ice at a temperature of —18° C. might still be liquefied by the 

 application of an enormous pressure. The following experiments 

 appear to show that a convenient manometer for very high pressures, 

 based on the observation of the freezing-point, may be easily con- 

 structed. 



In all the following experiments the galvanometer, moving to the 

 negative side, represents a cooling effect on the junction inside the 



* " The Effect of Pressure in Lowering the Freezing-Point of Water experimen- 

 tally demonstrated." " Phil. Mag.," 1850. 



