514 PROCEEDINGS OF THE AMERICAN ACADEMY. 



At the time that these disturbances were found no great confidence 

 was felt in the explanation that the effect was really due to the freezing 

 of the water. All of the compressibility measurements were made in 

 the presence of mercury. Now it had been already found that mercury 

 freezes under pressure, and at pressures very close to those actually 

 found. At 0°, for instance, the freezing pressures of water and mercury, 

 according to the final accurate determinations, are about 6400 and 

 7600 kgm. respectively, and these two transitions seemed much closer 

 together in the preliminary work because it was necessary to super- 

 press the water considerably before freezing begins, while the super- 

 pressure required for mercury is very small. It is true that there were 

 very great quantitative difficulties in the way of supposing the effect 

 due to the fi-eezing of the mercury, but still the neighborhood of the 

 mercury freezing point produced a sensation of disquietude. 



In order to definitely rule out the possibility of complications from 

 the neighborhood of the fi-eezing point of mercury, a form of experiment 

 was devised in which there was no mercury present. This was the 

 experiment also briefly alluded to in the introduction on the electroly- 

 tic conductivity of water. The water was placed in a shell of steel or 

 glass, and the conductivity measured between two concentric brass 

 cylinders attached to the insulating plug and suspended in the water. 

 The pressure chamber was filled with kerosene by which pressure was 

 transmitted directly to the water. There was no mercury anywhere 

 about it. The water was not absolutely pure, ordinary tap water being 

 used, which was sufficiently conducting for the purpose. In one case 

 distilled water with 1/10 per cent HCl was used. The resistance was 

 measured with a Kohlrausch bridge and a telephone in the usual way. 

 At high pressures there was unmistakable evidence of some sort of 

 change. The electrolytic resistance at first decreased with rising 

 pressure, passed through a flat minimum, rose slowly, and then very 

 rapidly to several times the former value, the rapidity being such as to 

 be almost equivalent to a discontinuity. This pressure of sudden rise 

 was taken as the freezing pressure, since it would be natural to suspect 

 the solid incapable of conducting. The pressure of transition was 

 measured in this way at several temperatures. In all, three sets of 

 readings were made with different forms of apparatus, and the last one 

 six months after the first. In the last determination, the existence of 

 the effect independent of the mercury having been already established, 

 the water was enclosed in glass with a mercury seal, the more effect- 

 ively to prevent absorption of impurities from the kerosene. The three 

 sets of determinations gave perfectly consistent results. A brief state- 

 ment as to the existence of a new variety of ice as proved by these 



