462 



Notices respecting New Book) 



of melting-point data are given. In all probability the ten- 

 dency to form molecular groupings and other unknown factors 

 tend to obscure the effect on melting-points due to the change 

 of constitution alone. 



Another point which I think may be noticed with advan- 

 tage from the series just given on page 461, and which, as far 

 as I am aware, has been hitherto neglected, is the effect on 

 the boiling-point of the symmetry of the molecule, uu sym- 

 metrical molecules tending to boil higher than symmetrical 

 ones. 



Consider the series A 1? page 461. Between the first and 

 second members of the series there is a large difference, the 

 molecular weight being increased and the symmetry of the 

 molecule destroyed at the same time. Between 2 and 3 of 

 the same series, on the other hand, there is a much smaller 

 difference ; the molecular weight is increased but symmetry 

 is restored, and the two things act against one another. 



Again, consider the series B x . Between 1 and 2 in this 

 series the destruction of hydroxy 1 lowers the boiling-point, 

 the destruction of molecular symmetry tends to raise it, the 

 result being that the difference only of the two effects is small. 

 Between 2 and 3 the destruction of hydroxyl and the resto- 

 ration of symmetry act together, and the resultant effect is 

 large. 



The same effects may be noticed by comparing A 2 and B 2 

 in the same way, and also by comparing the first, second, and 

 fourth members in the series A 3 and B 3 respectively. 



XLV. Notices respecting New Boohs. 



An Elementary Treatise on Modern Pure Geometry. 

 By E. Lachlax. (London : Macmillan. 1893. Pp. x+288.) 



ME. LACHLAN is a recognized master of the Geometrical 

 craft, and the work before us well maintains his reputation. 

 His primary object is to meet the new Cambridge Tripos regula- 

 tions, in which provision is made for the introduction of a paper 

 on " Pure Geometry/' All that could fairly be looked for in such 

 a paper is given by the writer, or is led up to by him. He has not, 

 however, contented himself with such a limited supply as this 

 would require, but he has written with a view to allure students 

 on to the arcana of the science. After a careful perusal we have 

 detected very few errata. On page 53, Ex. 4 is obviously a slip, 

 and in line 3 from bottom for Bx read By, for Cr read Cz. 

 Page 55 line 13 contains a small clerical error: the opening 



