1885.] Heat of Dissolution of Salts in Water. 401 



systems are of two sorts, viz., a point may lie on or off a line. We 

 may therefore graphically represent such a system by using two sorts 

 of graphical units, a pair of which, one of each sort, are either " con- 

 nected by a link or not, according as the point represented by one 

 lies on the line represented by the other or not. The laws regulating 

 the distribution of the links are stated, and the various forms which 

 collections of three and four points and collections of three lines can 

 assume are considered. 



§§ 362—375. Collinear Points. 



From the results of the sections under the preceding heading the 

 form of a system of collinear points is deduced. It is shown to be a 

 triadic group. The forms of tetrads of points of the system, both 

 harmonic and anharmonic, are discussed. 



§§ 376 — 380. Ordinary Algebra. 



From the preceding sections we naturally pass to the ordinary 

 algebraic treatment of collinear points, and the nature of quantities. 



§§ 381 — 387. Coplanar Points and Lines. 



These admit of discussion as a double system. The distribution of 

 the connecting pairs of the two systems is denned, and the algebraic 

 treatment deduced. 



§§ 388 — 389. Coplanar Points, Lines, and Conies. 



These sections refer briefly to the nature of the treble system com- 

 posed of coplanar points, lines, and conies. 



§§ 390—426. Logic. 



The memoir concludes with the considei^ation of the forms of 

 systems of which the units are classes. The investigation leads to a 

 recognition of the fact that on certain points a modification of the 

 views held by modern logicians is necessary. 



IV. "On the Influence of Temperature on the Heat of Dissolu- 

 tion of Salts in Water." By William A. Tilden, D Sc. 

 Lond., F.R.S , Professor of Chemistry in the Mason College, 

 Birmingham. Received May 18, 1885. 



The experiments described in this paper were undertaken in the 

 hope of obtaining some light upon the vexed question of the condition 

 in which a solid exists when dissolved in a liquid, and were directed 

 more especially towards the investigation of the well-known remark- 

 able phenomena exhibited by sodium sulphate. 



