luteUiyeiice and MUeellaiieoas Articles. 77 



some of enarmoiis size. The extent to which voloatiic materials 

 enter into the rocks of the district is romark.ible. 



The authors endeavoured to carrelaie the stratified rocks, and 

 adduced evidence to prove that the pebble and ash beds of Forest 

 Gate, the grit and pe')ble beds of the Hanging llocks, the similar 

 beds in the grounds of X. Ellis, Esq., at Swithland, and the 

 qnartzites of Bradgate-Stablc Quarry, Groby Pool, and Steward's- 

 Hay Spiing form one horizon, the slate breccias of lilores Hill, 

 B^adgate, Ulverscroft Mill, Markfield, Bardon, and High Towers a 

 second, the coarse ash-beds of Benscliff, Chitterman Hill, Tim.ber- 

 wood Hill, and the Monastery a third, and the quartzose rocks of 

 Charley Wood, Charley, the Old Reservoir, and Bl ickbrook a fourth. 



Hence they showed that the beds are considerably dislocated near 

 the syenites, which removes the main objection which previous 

 writers have urged against these being intrusive ; and they described 

 the evidence they have obtained as to this being their real nature. 

 This evidence included the description of actual contacts of igneous 

 and sedimentary rock seen at two points in the wood south of 

 Bradgate House, and at a third in Bradgate Park. 



They propose, in a continuation of the paper, to touch upon the 

 faults, ;ind to describe in greater detail the microscopic structure of 

 the rocks. 



X. Intelligence and Miscellaneous Articles. 



ON THE EQUILIBRIUM OF PRESSURE IN GASES. 



To the Editors of the PJiilosoj^hlcal Magazine and Journal. 



Gentlemei^, 

 ^pplERE is one point in connexion with my paper "on the Mode 

 -*- of the Propagation of Sound"*, published in the last Number 

 of your Journal, on which I would say a few words. As reerards 

 the process whereby the moiecuJes of a gas automatically adjust 

 their motions so as to move equally towards all directions, and thus 

 produce equilibrium of pressure, it should be stated, to prevent any 

 po.^sible misconception, that this depends (as deduced by Professor 

 Maxwell) on the oblique collisions of the molecules causing an equal 

 flow of vis iufci towards all directions, thus producing equilibrium 

 of pressure in all directions. 



The /Vcc^ that the molecules of a gas move equally towards all 

 directions (so that an equal number of molecules are moving in any 

 two opposite directions) was deduced by me from the observed fact 

 of the equiUbrium of pressure; but this deduction is not original, 

 inasmuch as the same fact had been previously deduced, without my 

 knowledge, by Professor Maxwell. 



I am, Gentlemen, 



Tours faithfully, 



London, June 8, 1877. 8. Tolvee Preston, 



* "' Mode of the Propagation of Sound, and the Physical Condition 

 Dftcrminiug its Velocity^ on the Basis of the Kinetic Theory of Q-ases/' 

 Philosophical Magazine, June 1877. 



