l54 SELECTED READINGS IN PHYSICS. KINETIC THEORY f(r)is therefore (ra) v Whence we may draw the following conclusions: Ist. The number of particles whose velocity, resolved in a certain direction, lies between x and x + dx is N v 2nd. The number whose actual velocity lies between v and u + du 4 N v2e-(o/adu 3rd. To find the mean value of D, add the velocities of all the particles together and divide by the number of particles; the result is mean velocity 4th. To find the mean value of u2, add all the values together and divide by N mean value of v This is greater than the square of the mean velocity, as it ougl