1887 .] Professor Tait on Smooth Impinging Spheres. 
85 
4. On the General Effects of Molecular Attraction of Small 
Range on the Behaviour of a Group of Smooth 
Impinging Spheres. By Professor Tait. 
(Abstract.) 
The present instalment traces some of the consequences of 
assuming the hard spherical particles of a gas to exert intense 
molecular forces when at distances comparable with their diameters. 
The effect of the new term in the virial in counteracting and at 
last obliterating that due to the impacts, is traced as the gas is 
gradually compressed. 
Next, the spheres (still supposed to attract one another) are 
regarded as capable of absorbing energy in a vibratory form, and 
of losing it directly by radiation. In such a case the relative 
translatory energy may be so reduced that pairs of spheres may 
remain within molecular distance from one another. The bearing 
of these results upon condensation, dissociation, &c., is given. 
PRIVATE BUSINESS. 
Mr Nanabhay A. F. Moos, L.C.E., B.Sc., Assistant Professor of 
Engineering, College of Science, Bombay, was balloted for, and 
declared duly elected a Fellow of the Society. 
Monday , 31 st January 1887. 
JOHN MURRAY, Ph.D., Vice-President, in the Chair. 
The following Communications were read : — 
1. On a New Formula for the Pressure of Earth against a 
Retaining Wall. By A. C. Elliott, B.Sc., C.E. Com- 
municated by Professor Armstrong. 
There are two main distinct methods of attacking the problem 
of the retaining wall. The first in chronological order is due to 
Coulomb, and is variously named, perhaps most commonly as the 
method of the Wedge of Least Resistance. Briefly characterised, it 
