Gaseous, Liquid, and Solid States of Water. 449 



ture and pressure which, in conformity with his language, may be 

 called the critical point of pressure and temperature jointly ; and 

 w# may see that, from any liquid state to any gaseous state, the 

 transition may be gradually effected by an infinite variety of courses 

 passing round the extreme end of the boiling-line*. 



The accompanying figure serves to illustrate these considerations 

 in reference to transitions between the three states, the gaseous, 

 the liquid, and the solid. The figure is intended only as a sketch 

 to illustrate principles, and is not drawn according to measure- 

 ments for any particular substance, though the main features of 

 the curves shown in it are meant to relate in a general way to the 

 substance of water, steam, and ice. A X and A T are the axes 

 of coordinates for temperatures and pressures respectively, A 

 (the origin) being taken as the zero for pressures and as the zero 

 for temperatures on the Centigrade scale. The curve L represents 



the boiling-line terminating in the critical point E. The line T M 

 represents the line between liquid and solid. It is drawn showing 

 in an exaggerated degree the lowering of the freezing tempera- 

 ture of water by pressure, the exaggeration being necessary to 

 allow small changes of temperature to be perceptible in the dia- 

 gram. The line T N represents the line between the gaseous and 

 the solid states of water-substance. The line LTN appears to have 

 been generally (in the discussion of experimental results on the 

 pressure of aqueous vapour above and below the freezing-point) re- 

 garded as one continuous curve ; but it was a part of my object in 

 the two British- Association papers referred to, to show that it 

 ought to be considered two distinct curves (L T P and N T Q) 

 crossing each other in the triple point T. 



In the second of the two British-Association papers already re- 



* Mention of this condition has been already made in a former paper bv mp, 

 in the * Proceedings of the Eoyal Society,' November 16, 1871, page 2. 



Phil. Mag. S. 4. Vol. 47. No. 314. June 1874. 2 G 



