THE 
LONDON, EDINBURGH, and DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
[FIFTH SERIES.] 
NOVEMBER 1883. 
XLVI. On certain Molecular Constants. 
By Fbedeeick GKttheie.* 
[Plates IV. & V.] 
Path-density. Path-mass. Liquid Slabs. Metallic 
Diffusion. 
§ 1. JDATH-DENSITY.— For some years past I have 
been trying to make clear to myself and others 
the idea of path-density as distinguished from ordinary den- 
sity. One is reluctant to introduce new conceptions into 
science unless they are called for by existing known facts, or 
unless they suggest the existence of unknown ones. The 
idea of path-density arose from the attempt to get an insight 
into the condition of the common surface of two media, and 
especially of that imperfectly understood condition of the 
surface of liquid masses, known as Surface-tension or Skin, 
The connexion between path-density and surface-tension will 
be shown in § § 13, 14. 
§ 2. If a given mass of matter alters its volume, it thereby 
alters its density. If a point or minute piece of matter which 
weighs a gram were to swell to the size of a cube centimeter, 
or if a cube yard of matter weighing a gramf were to shrink 
to the size of a cube centimeter, matter of unit density would 
* The experimental parts of this paper were communicated to the 
Physical Society during the Session 1882-83. 
t I use the terms "gram asweight" and "gram as mass' 'indiscriminately. 
Phil. Mag. S. 5. Vol. 16. No. 101. Nov. 1883. 2 A 
