BRIDGJL^N. — WATER UNDER PRESSURE. 451 



values on the parabola, to find the displacements at equal pressure 

 intervals. This has the advantage of giving a curve perfectly smooth 

 to the last of the significant figures. Curves thus obtained for the dif- 

 ferent temperatures were then combined by plotting the displacement 

 corresponding to the same constant pressure against the temperatures 

 of the different curves, and smooth curves were drawn through these 

 points. This last step could be made entirely graphically, since the 

 change of displacement with temperature at constant pressure is 

 comparatively slight. From these two sets of smooth curves, the dis- 

 placement for uniform pressure intervals of 800 kgm. and uniform 

 temperature intervals of 5° was found over the entire region. These 

 points were found in this way for each of the three experiments, that 

 with water and the two auxiliary ones, and the difference of displace- 

 ment at corresponding pressures and temperatures combined in the 

 way already described. 



The actual data above and below 0° follow. All the details of the 

 calculation of the compressibility at 0° and 22° by the first method 

 were the same as that used for determining the compressibility of 

 mercury. In fact, the two determinations, compressibility of water 

 and compressibility of mercury, were made at the same time and each 

 involves the other. It is to be noticed that the various disturbing 

 factors due to irregularities in the behavior of the steel bottle are much 

 less important in the case of water than they were in the case of 

 mercury. This is because of the higher compressibility of water as 

 compared with that of the mercury. Nevertheless, the effect of these 

 irregularities was distinctly felt here also, particularly if the pressure 

 had been allowed to reach so high a value as to freeze the water. The 

 best results were obtained with piezometers in which the water had 

 never been allowed to freeze. 



At 0"^, four different piezometers were used, one before and after 

 annealing, so that there are really five independent sets of determi- 

 nations. Three independent points with a sixth piezometer, No. 1, 

 were also found, but were not used in the computations, because this 

 was the very first trial ever made of the method, and the piezometer 

 had been badly strained by a pressure considerably beyond the freezing 

 pressure, the existence of which was not then suspected. The actual 

 data are given in Table I. To afford a comparison of the regularity of 

 these results as against the values obtained for mercury, the actual 

 points for the second best piezometer. No. 6, are shown plotted in 

 Figure 1. If comparison be made with the mercury points it will be 

 seen that these of Figure 1 are distinctly better. The changes of 

 volume at even pressure intervals, obtained from smooth curves from 



