49 



Ist. Ou upliill grade : 

 No. 1 odometer : Number of revoliitious = 997 = 399.52 revolutions per mile. 

 No. 2 odometiT : Nmiihi'i- of revolutions = 990 = 399.12 revolutions per mile. 



2d. Uu downhill grade : 

 No. 1 odometer: Number of revolutions =99."> = 398.72 revolutions pi r mill'. 

 No. 2 odometer : Number of revolutions = 1,000 — 400..'52 revolutions per mile. 

 Average, 399.27 revolutions per mile. 



BETWEEN CAMPS FOURTEEN AND FIFTEEN. 



Between mile-posts, measured by eliain, on a hard, somewhat rolling and sligiiUy sandy road, 

 l)rincipally down grade. 



liovolulious. 



No. 1 to No. 2 402 



h'cviiliilions. 



No. 4 to No. ') 4(»3 



No. 5 to No. (} 401 



No. 6 to No. 7 402 



No. 2 to No. 3 402 



No. 3 to No. 4 402 



Average, 402 revolutions. 



In remarking upon the results from odometer measurements, two distinct statements must be 

 made, 1st, that the vehicle should go always at a walk, since, by increasing the gait, certain irreg- 

 ularities of revolution must necessarily occur that will vitiate the measurement ; 2d, that the fric- 

 tion on the axle must be thrown out as being an element not easy to determine, and one not 

 iutiueucing the result in any appreciable degree so long as the axles are kept in anything like decent 

 order. The experiments made near Uamilton show that the results are e(iuable, both in the case 

 of using the axles after a three days' march, or a little more than sixty miles, and when freshly 

 greased, going to show tliat at least it, has not been necessary to take into account the idea of fresh 

 or newly greased wheels. 



It will be seen that in the revolution of a wheel by a horizontal pull that the length passed 

 over will exceed the circumference of the wheel on account of the slii)ping or sliding motion. It 

 can well be understood that this slii)piiig will be greater in case of rai)id revolutions ; another 

 reason that these measurements should be made at a walk. The allowance to be made for a slip, 

 determined by experiments made on an Arizona trip in 18GS, varieil from 1.2 to 2.1 per cent., 

 while the rigid tests of this year decrease this even to the making the mean allowance nearly per 

 cent. I refer this to the fact that in the lirst instance the aniui lis were ilriven at a tr>>t. Hence 

 the actual number of revolutions to the mile should be less than the number obtained by using the 

 perimeter as the basis; this is found iu practice to be the case, and obtaius in all our tests except 

 one at both Elko and Ifaby, and those between camps 14 and I.".. The former were nndimbtedly the 

 result of errors of observation; the later arises from the fact that the tire having become worn, 

 the perimeter was shortened. Omitting, then, these three cases, we have the percentage to be 

 allowed for the slii) as follows, viz: 



Experiments in Ruby Valley on haul rolling road O.li per cent. 



Experiments in ]{uby Valley on level rolling road 0.4 per cent. 



Experiments near 11 iinilton on steep-grade road 0.34 



3)0.98 



Average 0.33 per cent. 



All other things being equal, the slip of the wheel will vary aci^ordiug to the nature of the 

 road, increasing as the road bed l)eeomes more heavy, and in very heavy sand special allowance 

 has to be made. 



The slip of the wheel for up-grade is found to be greater than for down-grade. 



For the tirst part of the season 401 was the number of revolutions used per mile ; later it was 

 found that 400 was a preferable number. 



So great was the accuracy of these measurements that, taken in connectiou with the fact that 

 a Casella reconnaissance theodolite was used for the meander of the road traversed, it was unneces- 

 7 W 



