506 MEMOIR OF DAXIEL TKEADWELL. 



velocity was taken from my own minutes. It may seem to have been a neglect that no regular entry 

 was made of the elastic force of the steam. But the imperfection of the common safety-valve for measur- 

 ing this force is well known, being in fiict wholly fallacious, and, moreover, the object of immediate inquiry 

 did not render a constant knowledge of tiiis force necessary. I may remark that the steam was kept at 

 about GO pounds to the inch, as shown bj- the safety-valve. 



To find in these experiments the resistance from friction, and all sources other than tliat derived 

 from the inclination of the road, we may consider the whole road as forming one plane, and take the level 

 ofFramingbam above that of Boston as giving its inclination. Tlie diti'erence in these levels is IGO feet, 

 and the distance from one to the other 20J miles, or 108,240 feet. Hence lo^^g^-min 676, or a plane 

 rising one foot in G76 would unite the two levels, and the force required merely to elevate any loatl over 

 such a plane would be equal to 5 15th part of the weight of the load. 



To apply this to the foregoing experiments, the load being 96,103 lb., we have ae}ga= 142.1 lb. of 

 the draft from elevating the load, and the mean force of the whole traction as shown by the dynamometer 

 was 518 lb.; then .")18- 142.1 = 375.9 lb., as the resistance from friction and all other sources than that 

 of elevating the load. Again, "jiu,"^ =255, or the traction from friction was equal to jijth part of the 

 load. Hence the resistance from this source was 8.78 lb. to every ton of 2,240 lb. of load. 



By the same method the resistance from friction may be found on the return ; but as the load 

 descended through a space equal to ci^th part of the space passed through, we must add jl^th part of the 

 weight of the load to the mean force of traction, as shown by the dynamometer, to obtain the resistance 

 of the friction. We have, then, the load being 91,795 lb. for the return, a^IJi = 135.8 lb. for the 

 effect of the tendency of the load itself to descend, ilean draft on the dynamometer 310.6 lb. Then 

 135.8-1-310.6 = 446.4 lb., the resistance of the friction. Again, ifV(rY = -06, or the resistance from 

 friction was equal to 206 lb. of the load. Hence on a level, according to this experiment, the force of 

 traction was 10.87 lb. for each ton of 2,210 lb. 



It will be observed tiiat in all tiie trials, with a single exception, the traction on the return, or down 

 the plane, when reduced to a level, as in the foregoing example, was greater than the traction out or up 

 the plane. This small discrepancy is to be attriliuted to the fact that the dynamotneter did not indicate 

 negative quantities, which it might easily be made to do, and on some of the steep descents the train bore 

 hard upon the tender and the engine ; for the friction of these being greater tlian that of the cars com- 

 pared with their weight, a portion of the descending force of the latter was transmitted to them through 

 the dynamometer, where, if it had been measured as a negative quantity, I have no doubt but the experi- 

 ments in the two directions would have shown a much more exact correspondence. From this statement 

 it will be perceived that the resistance of the friction as deduced from the experiments made up the plane 

 is to be considered as the true measure, and should be taken as such by any one who is desirous of ob- 

 taining the absolute amount of this resistance. 



2. Experiment made, October 15, with the Mercury, without the sparker, from the depot in Boston 

 to Framiugham. 



Load oit Tuain. 



Tender Xo. 4. 



9 cars loaded witli iron rails Weight, 77,53d lb. 



1 car loaded with stone 9.210 



1 car carrying apparatus and 4 persons 5,050 



Whole weight, 91,795 lb. 



Wood used, being pine of ordinary quality. Out, 67 cubic feet measured as ordinarily piled. Return. 43.7 

 cubic feet. 



Water used. Out, .52 cubic feet. Return, 40.G cubic feet. 



Wood required to ev.iporate one cubic foot of water. Out, 1.27 cubic feet. Return, 1.20 cubic feet. 



