17 
Ordinary Meeting, October 20th, 1885. 
Chaeles Bailey, F.L.S., in the Chair. 
Professor Reynolds, F.R.S., exhibited his experiments 
showing the Dilatancy of granular material, which formed 
the subject of a paper read before Section A at Aberdeen, 
which paper will appear in the December numAer of the 
Philosophical Magazine, an abstract having already appeared 
in Nature, Oct. 1. A paper was then read. 
“On the Velocity with which Air rushes into a Vacuum, 
and on some Phenomena attending the Discharge of Atmos- 
pheres of higher into Atmospheres of lower Density.” By 
Heney Wilde, Esq. 
Considering the present condition of our knowledge 
respecting the mechanical properties of air and other 
gases, some apology might appear to be needed in bringing 
before this Society the results of an investigation touching 
some fundamental principles in pneumatics, which, for 
more than a century, have been considered to rest on 
foundations as secure as the laws of gravitation of the 
heavenly bodies. A survey of the history of the dynamics 
of elastic fluids will, however, show that great as are 
the advances which have been made in this branch of 
science, the laws of the discharge of elastic fluids, under 
the varied conditions of elasticity and volume are still left 
in much obscurity. The several circumstances which have 
combined to produce this anomalous state of our knowledge 
Proceedings — Lit. & Phil. Soc.~Yol. XXV.—No. 2.—Session 1885-6. 
