34 Proceedings. 



Ordinary Meeting, November 29th, 1893. 



Professor Arthur Schuster, Ph.D., F.R.S., F.R.A.S., 

 President, in the Chair. 



The thanks of the members were voted to the donors of 

 the books upon the table. 



Professor Lamb, M.A., F.R.S., made a communication 

 giving a mathematical explanation of the mode of propaga- 

 tion of waves through water by a moving object. 



Mr. C. H. Lees read a note on the determination of the 

 thermal conductivity of water. 



Mr. Harry Grimshaw, F.C.S., read a paper " On the 

 treatment of sewage with basic persulphate of iron under 

 varying conditions, more especially with regard to results 

 obtained in Salford." From the experiments he concluded : — 

 That the Salford sewage in June, 1893, was, m consequence 

 of the long-continued drought, about 25 per cent more 

 impure than the average. That while it is possible to vary 

 the proportion of precipitants to such wide differences as 

 exist between night and day sewage, it is not practicable 

 on the large scale to meet the hourly fluctuations in the 

 composition of the sewage of an industrial town ; during the 

 working day, therefore, the maximum amount must be 

 adhered to. That a too rapid flow through the tanks 

 involves a greater expenditure of precipitants than is other- 

 wise necessary, and that a flow of an average of about 

 10,000,000 gallons, or a maximum of 14,000,000 gallons, 

 through tanks of a vertical area of Soft, by 7ft. renders 

 proper subsidence impracticable. That in cases of this 

 kind the only remedy is either the use of excessive amounts 

 of precipitants or the subsequent passage of the tank 

 effluent through a straining filter or through land ; which 



