BULLETIN OF THE UNITED STATES FISH COMMISSION. 149 



liypothetically perfect diagram is marked, and if an engineer is willing 

 to accept them as the ultima thtile he will doubtless decide in favor of 

 that produced by the engines as originally arranged, namely, at 145 de- 

 grees crank angle. 



The indicator is the stethoscope of the steam cylinder only ; it fails 

 to give any indication of the work, either utilized or wasted, beyond 

 the steam cylinder. 



It is manifest that a crank turned by a uniform moment is revolved 

 with less labor and less injury to its journals than if turned by an in- 

 termittent force ; by blows for example. Uniformity of torsion on the 

 shaft is one of the great objects sought. This torsion may be demon- 

 strated, graphically, by constructing diagrams whose abscissa is re- 

 ferred to the length of the path of the turning force, and the ordinates 

 to the moments of torsion. In Figs. 1, 2, and 3, the ordinates are cal- 

 culated for the combined moments of the two cranks, the same units be- 

 ing used for each. The lines c d, in these figures, refer to the path de- 

 scribed by the combined eflbrt of the two cranks, and the ordinates, 

 commencing with a h, and ending with a' 6', represent the moments of 

 torsion. The curved lines represent the variation in the torsion, and 

 the superiority of these torsion curves is in their nearer approach to 

 the straight line c d. 



This graphic method might be pursued still further by applying a 

 dynamometer to the screw shaft, which would indicate the thrust of the 

 screw, wherein every increment or diminution in that force would cor- 

 respond with those in the torsion diagram, but would be greatly re- 

 duced in extent owing to the weight and consequent inertia of the 

 heavy working parts. 



In changing the crank angle from 145 to 90 degrees the eccentrics 

 were not disturbed ; the cushioning, lead, and release are the same in 

 both cases; the same boiler-pressure and mean back-pressures are main- 

 tained, and the same number of expansions are employed; consequently 

 there can be no i^hysical advantage in the original over the present 

 crank angle. The mechanical saving in the minute amount of friction 

 eliminated in a single journal of each engine is much more than com- 

 pensated lor by the saving of friction on the screw blades alone, by 

 their more uniform velocity. 



The Katzenstein packing on the piston rods has worked so well that 

 I feel it merits a special mention. I respectfully recommend it be placed 

 on the H. P. valve stems. The Baird distilling apparatus has pro- 

 duced 5,883 gallons of water during the quarter, steam being used from 

 the main boilers, the ship being at sea under steam, and cylinder oil (a 

 compound of petroleum) being used in the cylinders ; the water was 

 good. The anemometer used in measuring the air currents in our ven- 

 tilating tubes broke down, but the makers replaced it with a new one, 

 since which time I have been recording air velocities, and hope, at the 

 end of the next quarter, to be able to report on the ventilation of the 

 ship. 



