Then calculate the value of the live-load reaction for the maximum stress in each web-member by means of the slide-rule and the following formula and table, in which  n  is the number of panels in the span,  n'  is the number of the panel point at the head of the train, counting from the loaded end of the span, and  C  is the coefficient of

Live-load reaction for the head of train at

Then, still using the slide-rule, find the greatest live-load stress in each web-member by the following equation:

Stress required =

Where the panels are divided as in the Petit truss, and where inclined subposts are employed, the tensile stress in the upper half of each main diagonal thus found will have to be corrected by subtracting therefrom a stress equal to L / 2 sec A, where A is the inclination of the diagonal to the vertical. But when inclined subties are used instead of inclined subposts, the correction just referred to will apply only to the compressive stresses in the lower halves of the main diagonals. The reason for making this correction, as will be at once evident to any one who is accustomed to finding stresses in Petit trusses, is that the method above outlined ignores the subdivision of the panels when ascertaining by graphics the stresses caused by the assumed upward reaction.