20 REVOLUTIONS OF ENGINE. [CHA.P. I. 



but, on the other hand, the vibration caused by the machinery 

 increasing also, much to the discomfort of the passengers. 



Among the wonders of the engine-room, no object made so 

 lively an impression on my mind as a small dial, called the 

 Indicator, where a hand, like that of a clock, moving round in a 

 circle, registers the number of revolutions made by the wheels of 

 the engine during the whole voyage ; this hand or index being 

 attached to one of the moving shafts, and made to advance 

 slightly by every stroke. We were going at the time at the 

 rate of ten and a half miles an hour, and the paddle-wheels 

 were revolving fifteen and a half times a minute ; but during the 

 gale they had only made six or seven revolutions, the engineer, 

 to avoid too great a strain on the machinery, having then burned 

 much less coal, and going no more than half speed. Our short 

 est day s sail, during the whole voyage, was 114 miles. I 

 observed, on our arrival at Boston, that the number of revolu 

 tions registered by the Indicator was 275,122, the ship having 

 run 2946 miles in fourteen days and twenty-two hours ; the 

 distance from Liverpool to Halifax being 2550 miles, and from 

 thence to Boston 396. For the sake of comparing this result 

 with former voyages of the Britannia, I made the following 

 extract from the Log Book of the chief engineer : 



Number of Length of 



Revolutions Voyage. 



of the Engines. Days. Hours. 



Outward Voyage, May. 1845 .... 273,328 .... 14 12 



Homeward do. June, &quot; .... 253,073 .... 11 8 



Outward do. July, &quot; .... 282,409 .... 18 13 



Homeward do. August, &quot; .... 292,122 .... 14 2 



It is remarkable how nearly the number of strokes made by 

 the engine in our present voyage agrees with those recorded in 

 the voyage of last May, which it will be seen was of the sarn,e 

 length, with the exception of a few hours, the longer voyage 

 exhibiting a slight excess in the number of revolutions. In all 

 the four trips, the difference between the highest and lowest 

 numbers, amounts to no more than a seventh or eighth of the 

 whole. It is like the regular pulsation of the heart, beating a 

 given number of times in a minute ; the pulse quickening during 



