In still rarer cases both a leading and a trailing bogie have been fitted.
Aspinall on the Lancashire & Yorkshire railway to ascertain the resistance of trains of bogie passenger carriages of different lengths at varying speeds, and the results are recorded in a paper, " Train Resistance," Proc. Inst.
per hour: - rv= 3.58-I 165S(I 61S } 50) for 4-wheel coaches, (13) 1000 rv= 3-58+ I 645(1 61S +IO) for bogie coaches.
17, four values of L being taken for formula (12) corresponding to trains of 5, 10, 15 and 20 bogie carriages.
Thus 4-4-2 represents a bogie engine with four-coupled wheels and one pair of trailing wheels, the wellknown Atlantic type; 4-2-2 represents a bogie engine with a single pair of driving-wheels and a pair of trailing wheels; 0-4-4 represents an engine with four-coupled wheels and a trailing bogie, and 4-4-o an engine with four-coupled wheels and a leading bogie.