TrIE bureau is conducting an extensive research on coal-mine ventilation factors. After the resistance of an unobstructed entry to flow of air had been determined by tests in the Experimental Mine, mine cars were run into the test section in various arrangements and the increase in resistance was determined. Tests were made to determine the effect of : (I) Varying the number of cars in a trip; (2) varying the position of the trip ; (3) varying the distance between cars; and (4) varying the size of a car. Tests were also made to compare the resistance of empty and loaded cars, and to compare the resistance of cars when in unbroken entry and when opposite to cut-through dead ends. It was found that the "end " resistance of a single car was three times the " side " resistance, and, consequently, 75 per cent. of the total resistance. The end resistance will probably vary as some power of the ratio of end surface area of the car to the cross-sectional area of the entry. The side resistance will vary with the length of the car, the character of the surfaces over which the air rubs, and inversely with some power of the clear area left for the passage of the air. Further research is necessary to determine these relations exactly.
When two or more cars are coupled together, the end resistance is the same as that of a single car. The side resistance, however, is the resistance of a single car multiplied by the number of cars, and the total resistance is the sum of the end and side resistances, assuming a uniform entry in all cases.
When two cars which have been coupled together are moved apart, the resistance increases to a maximum at about twenty-five feet between bumpers.
The difference in resistance between loaded and empty cars was of no practical significance, and cars had the same resistance when in unbroken entry and when opposite cut-through dead ends. The resistance caused by cars was independent of the veloe-* Communicated by the Director. 833