70 Teansacttoxs of the Amebic an Institute. . 



shaft alono, and also with its belt thrown off. The difference 

 between the two should have given the power required to drive the 

 shaft wlien subject to the tension of the particular belt in use. In 

 making this trial, however, the wishes of the exhibitors were regarded, 

 and the diagrams taken with full boiler pressure in the steam chests, 

 the regulation being performed b}' the governor, so 'as to take 

 account also of the friction of the valves under the circumstances of 

 regular working. The resulting diagrams were nearly all negative, 

 showing that the indicator could not be relied on to measure the 

 j)Ower at such extremely short points of cut off, as were required 

 merely to overcome the friction of the engines. Upon discovering 

 this, a new set of friction diagrams were taken by regulating with 

 the throttle, and thus producing a more uniform pressure in the cyl- 

 inder. The last of these were taken late at night, after the last of 

 close of the exhibition for the season, so that there was no time to 

 replace the belts and try the friction of the shaft in the same manner. 



Having, however, both the indicated and dynamometer horse- 

 power, the friction of this shaft in the two cases, has been found in 

 another way, shown in " table No. 2," under the head of the " dis- 

 tribution of power." From the indicated horse-powder (line h) is first 

 subtracted the friction of the engine, per indicator (line i\ and the 

 remainder is the gross load (line^*.) The extra friction caused by the 

 transmission of this load would usually be reckoned at seven and a 

 half per cent ; but in these cases, I am satisfied that it was much less, 

 for the reason that during the trial the lubrication was very well 

 attended to. The low co-efficient of four per cent has, therefore, 

 been used to obtain the friction of the load- (line Jc\ which is sub- 

 tracted from the gross load, and the remainder (line m) equals the 

 net or effective horse-^ower, transmitted through the belt, or in other 

 words, the useful work done. From this i% substracted the dynamo- 

 meter horse-power (line n), and the remainder equals the friction of 

 the connecting shaft (line o\ which shows that, by actual measure^ 

 the friction of the shaft when the belt of the Eabcock and Wilcox 

 engine was in position, M'as much greater than when the belt of the 

 Harris engine was in use. 



Line ^>, shows the average amount of water per hour pumped into 

 the boilei*s as measured by the meter. 



Line q^ shows the quantity of water used as calculated in the usual 

 manner from the weight of the steam at the mean terminal total 

 pressure shown by the indicator diagrams. 



