384 Proceedings of the Royal Society of Edinburgh. [Sess. 
In conclusion, the author begs to state that this research was suggested 
to him by Dr J. H. Smith, Professor of Mechanical Engineering at the 
Belfast Municipal Technical Institute, who was of opinion that a thorough 
experimental investigation of the subject would be of service to people who 
were chary of using the formulae they could not prove, or for which no 
proof was obtainable. 
The author desires also to express his thanks to Professor Love and to 
