Introducing these quantities into equation (33), and remembering that the train moves on to the bridge from _A_, it would be found that the second axle of the first locomotive must be placed at the section _Q_, as shown in Fig. 25_d_, which exhibits the lower-chord panel-points numbered from 1 to 7. The conventional unit load _g_ will be taken in this case at 20,000 pounds. It is represented as _AG_ and _BF_ (Fig. 25_d_), laid off at a scale of 10,000 pounds per inch. _K_ is immediately under panel-point 5 and _L_ is immediately above panel-point 6, hence the broken line _AKLB_ is the influence line desired. The vertical lines are then drawn from each train concentration in its proper position, all as shown, including the vertical line through the centre of the 54 feet of uniform train-load on the left. The summation of all the vertical intercepts between _AB_ and the influence line _AKL_, having regard to the scale and to the ratio between the various loads and the unit load _g_, will give the following tabular statement: .22 × 54 × .2 × 10,000 = 23,760 pounds. 2.2 × 1.3 × ” = 28,600 ” 3.02 × 2 × ” = 60,400 ” .9 × 1 × ” = 9,000 ” 4.06 × 1.3 × ” = 53,780 ” 4.53 × 2 × ” = 90,060 ” .5 × 1 × ” = 5,000 ” -------- 2⟌ 270,600 ” -------- Shear for one truss = 135,300 ” These simple operations illustrate the main principles of the method of influence lines from which numerous and useful extensions may be made. CHAPTER IX.