168 Proceedings, &a, for 1885. 



drains. This difficulty was very successfully met by means of the 

 Shore system. An air compressor was erected 1J miles inland, 

 and compressed air at about 10 lbs. pressure is carried to the 

 town in pipes opening into two large tanks. "When the tide is 

 high the sewers discharge into one of two large receivers sunk in 

 the beach. When this one is full a valve is opened, and air comes 

 in, forcing the matter out to sea. The set of the current is such 

 as to carry all the matter out to sea, leaving the beach clean. 



It is much to be desired that we may ere long see some such 

 method as has been described in use in Melbourne. Surely no 

 justification can be found for such wilful pollution of one of the 

 finest streams in the colony as is carried on at the present time. 



June 2ith, 1885. 



Kainfall and Flood Dischakge. Mr. G. R. B. Steane, C.E. 



There was a small attendance at this meeting, owing to the 

 inclement weather. 



Discussion on Mr. Steane's paper was postponed to the next 

 meeting. 



Mr. C. W. M'Lean exhibited a very novel instrument known 

 as the " Metacentre Balance." This was also shown later on at an 

 ordinary meeting of the Society, so there is scarcely any need of 

 further description in this place. 



The present state of the science of hydrology is very unsatis- 

 factory indeed. Authorities differ as to whether we should call 

 the maximum rainfall \ inch or 1 inch per hour. It is not 

 difficult to make the dimensions of waterway excessive ; the great 

 problem is to make them just sufficient, no more and no less. 

 Merely to gauge a stream with a view to constructing permanent 

 works is very unsatisfactory, for improved drainage may entirely 

 change the aspect of the question, giving rise to the need of large 

 waterway. A careful study must be made of the rainfall of the 

 district under notice — of the nature of surface and. inclination of 

 the channel. Thus, sandy loam and chalky ground act very 

 differently. The rate of discharge will increase with the rainfall, 

 the area (within certain limits), the slope of the ground, and 

 improved drainage. It will decrease with the increase of reservoirs 

 and the porosity of the ground, and also as the ratio of the length 

 to width of the drainage area increases. 



It is worthy of notice that a rainfall of 1 inch per hour over one 

 acre is equivalent to about 1 cubic foot per second. 



We must carefully distinguish between the cases of large and 

 small areas. Very heavy rains seldom last more than a few 



