1 86 ./ W. Gibhs—Equilibrluni of Heterogeneous Stihstances. 



(levelopable surface formed on the sheets (A) and (B), the surface of 

 dissipated energy will be altered in its general features only by the 

 removal of the single point of the sheet (C). But if the temperature 

 or pressure is altei-ed so as to make a part of the sheet (C) protrude 

 through the developable surface formed on (A) and (B), the surface 



b of dissipated energy will have the 

 form indicated in figure 8. It 

 will include two plane triangles 

 ABC and A'B'C, a part of each of 

 the sheets (A) and (B), represented 

 in the figure by the spaces on the 

 left of the line aAiV'a' and on the 

 \ right of the line bBB'b', a small 

 ^i«- 8- " part CC of the sheet (C), and de- 



velopable surfaces formed upon these sheets taken by pairs ACC'A', 

 BCC'B', aABb, a'A'B'b'. the last two being dilFerent portions of the 

 same developable surface. 



But if, when the primitive surface is constructed for such a 

 temperature and pressui-e that it has three points of contact with 

 the same plane in the same straight line, the sheet (C) (which has 

 the middle position) at its point of contact with the triple tangent 

 plane intersects the developable surface formed upon the other sheets 

 (A) and (B), the surface of dissipated energy will not include this 

 developable surface, but will consist of portions of the three primi- 

 tive sheets with two developable surfaces formed on (A) and (C) and 

 on (B) and (C). These developable surfaces meet one another at 

 the point of contact of (C) with the triple tangent plane, dividing the 



portion of this sheet which be- 

 c 7 longs to the surface of dissipated 



energy into two parts. If now 

 the temperature or pressure are 

 varied so as to make the sheet 

 ((3) sink relatively to the de- 

 velopable surface formed on (A) 

 b' and (B), the only alteration in 

 the general features of the sur- 

 face of dissipated energy will 

 be that the developable surfaces 

 formed on (A) and (C) and on (B) and (C) will separate from 

 one another, and the two parts of the sheet (C) will be merged in 

 one. But a contrary variation of temperature or pressure will give a 



