PHYSICAL PROPERTIES OF WATER, ETC. 5 l J 



1°-13 only per ton of additional pressure, — and has a start of but 4°, — the maximum- 

 density point will overtake it at about — 2° -4, under a pressure of 2 '14 tons. 



The diagram 2 of Plate II. shows the consequences of the pressure-shifting of 

 the maximum-density point in a very clear manner, — especially in its bearing on the 

 expansibility of water at any one temperature but at different pressures. The curves 

 in the diagram are for atmospheric pressure, and for additional pressures of 1, 2 and 

 3 tons respectively. They are traced roughly by the help of Despretz's tables of 

 expansibility at atmospheric pressure, and the compression data of the present 

 Report. The quantity of water taken in each case is that which, at 0° and under 

 the particular pressure, has unit volume. Thus all the curves pass through the same 

 point on the axis of volumes. How, in consequence of the gradual lowering of the 

 maximum-density point, the expansibility at zero, which is negative at atmospheric 

 pressure, and even at 1 ton of additional pressure, becomes positive and then rapidly 

 greater as the pressure is raised, is seen at a glance. 



I have to state, in conclusion, that my chief coadjutors in the experimental work 

 have been Mr. H. N. Dickson and my mechanical assistant Mr. T. Lindsa}'. Mr. 

 Dickson also reduced all the observations, about half of them having been done in 

 duplicate by myself. 



In the compression of glass I had the assistance of Mr. A. Nagel, and occasionally 

 of Dr. Peddie. 



Mr. A. C. Mitchell assisted me in the graphic work, and checked the calculations 

 in the text. 



I have already acknowledged the density determinations and analyses of sea-water 

 and salt solutions made by Dr. Gibson. 



And I have again been greatly indebted to the very skilful glass-working of 

 Mr. Kemp. 



[7/9/88. — The following analysis of the glass of my piezometers is given by Mr. 

 T. F. Barbour, working in Dr. Crum Brown's Laboratory : — 



