224 Trans. Acad. Sci. of St. Louis. 



The average value of c and the values of P and d' being 

 substituted in ( 1 ) the value of p for each value of d is com- 

 puted. These values are given in the third column of the 

 table. 



The vertical asymptote of the curve is inside of the car 

 surface a distance d' = 15.1 inches, and the limiting pressure 

 which would be observed if the collector were thrust far out 

 into the undistubed air is P — 3.42 lbs. per square foot. 



The measurements of the last table were made in the rear 

 of the fourth car from the locomotive. They covered the 

 distance from St. Louis to Burlington and return. The actual 

 distance covered while the measurements were being made was 

 316 miles, during 7.88 hours, not including stops. The aver- 

 age velocity of the train was 40.1 miles per hour. The aver- 

 age weighted v 2 was 1746. The square root of this value, the 

 virtual velocity, is 41.7. The constant in equation (3) is by 

 this determination 



P 3.42 



? = 1746 = °- 0020 - 



The velocity of the train was determined by timing its pass- 

 age through all stations which could be identified, and by 

 timing its arrival in and departure from all stations where 

 stops were made. During this trip the wind was very light 

 from the East while going from St. Louis to Burlington. 

 On the return trip the wind was from the N. W., with a 

 velocity of from 6 to 12 miles per hour. This would make 

 the effective velocity somewhat less than that of the train on 

 the return trip. 



A decrease of 4.7 miles per hour in the j/ mean square 

 velocity produced by a following wind, would account for the 



P 



reduction of the value of -* from 0.0025 to 0.0020. 



v 



The effect of a wind blowing transversely across the train, 

 in an open country, is to largely obliterate the phenomenon 

 of train draught. The air drifts away from the train too 

 quickly to be set into motion by the successive action of all 

 the cars in the train. The effect then appears and disappears 



