Last of the Paddle Liners 89 



tion of the tandem compound engine. 

 Here, as its name implies, the three cylin- 

 ders of the triple expansion engine were 

 placed tandem fashion. Mr. Macdonald 

 describes it as a perfect unit, not only 

 simple, but it provides perfectly for the 

 complete expansion of steam, and it can 

 be repeated according to the number of 

 cranks. 



Still another factor which helped for- 

 ward the steamship in the era we are con- 

 sidering was the greatly improved boilers 

 employed. The improvement in the 

 boiler was largely brought about by the use 

 of mild steel. In this way not only was a 

 stronger boiler obtained, but the thickness 

 of the plates was very much decreased. 



One more point we will notice before 

 we pass on to the history of the steamer 

 itself, and that is the introduction of forced 

 draught for the stokeholds. I need not 

 stay to describe the various systems 

 brought into use; the general principle 

 involved was that air was forced into the 



