504 [Proc. B.N.F.C, 



frozen, although their temperature is lower than freezing point. 

 It is amongst these clouds that the most beautiful and varied 

 forms of waved clouds are frequent, as the result of undulatory 

 movements in the atmosphere and irregularities of the earth's 

 surface. Cirrus and alto-clouds are largely produced by 

 multiplied columns of ascending, air of smaller extent and of 

 less force than those which produce Cumulus or common 

 Stratus. 



The lecture was much appreciated, and at its close Mr. 

 Fennell criticised the paper in an able and interesting speech. 

 The discussion was then taken up by Messrs. W. H. Patterson, 

 William Gray, Robert Welch, and Robert May. 



' GEOLOGICAL ASPECTS OF WATER SUPPLY. 



The Wednesday evening meeting was held in the Museum 

 on 23rd January — Professor Gregg Wilson in the chair — when 

 Mr. Andrew Duncan, B.Sc, of Queen's College, read a paper 

 on above. He said the question of water supply has not caused 

 Irish local authorities the same worry and trouble as it has 

 caused their neighbours across the Channel, the reason being 

 that in Ireland there are large gathering-grounds as yet un- 

 tapped from which immense quantities of fine water may be 

 drawn. As Ireland becomes more populous and prosperous, 

 however, and as her towns and cities develop, it is certain the 

 problem will begin to press rather heavily on her also. Two 

 great sources from which a community may draw a supply for 

 public purposes are surface waters and underground waters. 

 In many cases the poverty of the district in porous rocks makes 

 the provision of a supply from underground sources impossible. 

 In such circumstances recourse must be had to surface waters 

 and a supply obtained by utilising the waters of some river or 

 lake or by the creation of large impounding reservoirs. The 

 civil engineer, in considering any scheme for leading in a supply 

 of surface water, must make careful inquiries into' the amount 

 of the annual rainfall over the area constituting the gathering- 

 ground, and he must also bear in mind that the petrographical 



