PUMPING MACHINERY OP TUP WATER AND SEWERAGE BOARD. XLI. 



acting and rotative systems, there is not only a continually 

 varying ratio between the speeds of the steam and water 

 pistons but the mean speed per minute of the two ends is 

 not necessarily the same. Theoretically the Hatliorn 

 Davey differential system should be expected to give the best 

 results, and if the record of the Spottiswoode engine is 

 absolutely reliable, then it would seem to be borne out in 

 practice with a consumption of 131bs. of steam per HP hour; 

 but if the Marrickville outfit of same type takes 21 lbs. of 

 steam as stated, there is certainly an opening for further 

 explanation in the author's reply. 1 The duty recorded by 

 the trials at Marrickville of July 1900, are no better than 

 those of the old Orown-street engines, which were made by 

 Mort's Dock Engineering Co., and designed by the speaker 

 (Mr. Selfe), which were fairly worked to death before 

 removal. 



It is undoubtedly true, as laid clown by Herbert Spencer, 

 that we are all more or less actuated by unconscious bias, 

 and even one who, like the speaker, is not interested in 

 any particular type, may have predilections apart from 

 convictions based on indisputable tests. But unfortunately, 

 in these commercial days, when the business aspect of an 

 engineering installation often overshadows the professional 

 and technical one, the merits of special types are often 

 advocated by skilled salesmen ; and it behoves the innocent 

 man, who is merely a technical expert, to be on his guard 

 when the specious advocacy of any particular machine, 

 whether in print or by word of mouth, is put before him. 



So far it seems certain that the author of the paper is 

 quite correct when he places the multiple expansion rota- 

 tive pumping engine at the head of the list for steam con- 



1 Mr. Furniss explained in his reply that the Spottiswoode engines were 

 not of the differential type, but were triple expansion inverted marine 



type.— N.S. 



