The Antrim Gravels. 39 



With respect to the use of compressed air, and specially as 

 comparing it with hydraulic supply, for the use of motors : — 

 In the case of air, the ordinary steam engine, with unimportant 

 alterations, is used, so that the system may be applied to already 

 existing engines, whereas with water special machines have to 

 be provided. Again, air is elastic, and for varying loads on the 

 same engine can be used more or less expansively ; water, being 

 inelastic, each stroke of a hydraulic motor uses the same quan- 

 tity whether the load be light or heavy. The pipe friction of 

 water as compared with air is roughly in proportion to their 

 densities : taking the former as supplied at 700 lbs. of pressure 

 per square inch and the latter at 45 lbs., the ratio is as 200 to 1. 

 The energy contained in a cubic foot of water at that pressure is 

 but is}4 times that in a cubic foot of air worked even non-expan- 

 sively, or say eight times that of air worked to best advantage, 

 while its pipe, port, and valve friction is 200 times as great ; and, 

 lastly, in hydraulic high-pressure supply there is no reservoir ; — 

 the accumulators used can only hold a few seconds' supply ; — 

 whereas in air the whole of the mains laid in the streets form 

 a vast receptacle from which supply may be taken for a con- 

 siderable time without serious reduction in pressure. 



4th January, 1887. 



W. H. Patterson, Esq., M.R.I. A., in the Chair. 



The Rev. Canon Grainger, D.D., M.R.I.A., read a Paper on 



A QUESTION CONCERNING THE ANTRIM 



GRAVELS. 



Rev. Canon Grainger read a paper on "The Antrim 

 Gravels," referring to the absence of the characteristic 

 stratification near the surface of gravel hills, and attributing it 

 to the action of sub-glacial rivers at a late glacial period. 



Canon Grainger also exhibited a most interesting collection of 

 Chinese, Indian, and other antiquarian specimens, including a 

 magnificent set of jade axes and other instruments. 



