OEDINABY OSCILLATING PADDLK-WHEEL ENGINES. 21 



1-0 enter the harlioui'S," find " lying witli bnnked fires," tlierc 

 is no reliable (Lata available wlierebj tlio exact consumption 

 [)er liour at full speed could bo obt-ained without a special 

 trial, for which there was no opjiortunity. JSiit iis tliis vessel 

 has been uniformly employed upon the same service, this 

 will be quite sufficient to enable us to compai'o the results so 

 as to get at the economy of the tlu'ee systems. I should 

 .state thfit the consumption in each case lias been ari'ived 

 at by taking the average for twelve months. 



The rate of combustion is 15 lbs. per square foot of gi-ate 

 per hour, which was found to be the most economial rate 

 with natural draught (for wo have not arrived at forced 

 draught in this vessel yet), and for obvious reasons this is 

 the rate which has been maintained tliroiigliout. 



Under these circumstances then, the mean pressure in the 

 cylinders was 21^ lbs. per square inch, the engines made 30 

 revolutions per minute, and developed 1,605 indicated horse 

 power, giving the vessel a mean speed of 14i^„ knots per 

 hour, and a displacement coefficient of 194. 



These, then, are tlio conditions under which the iirst 

 ari-angoment of the macjhinory woi'lced for eiglit years. 



Then had to bo realized the fact experienced by all who 

 liave charge of the practical working of engines and boilers, 

 that whereas the engines were in a condition to still develop 

 their maximum ])owor, i)rovidod siifliciont energy was ap- 

 jjlied to the pistons in the shape of steam at good pressui'e, 

 on the other hand the boilers themselves were feeling the 

 effects of old ago, indi(^ating tluit it would be prudent to 

 allow them to retii'e from active service as soon as con- 

 venient ; so that, in common with the fate which awaits 

 niortids as well as ma,ehinery, they wore gracefully retired, 

 and eventually found a resting-place on the scrap heap. 



This, then, brings us to the year 1875, and to the consider- 



