selves with full force upon the levers, the result being the same as before. The author stopped this instantly, and upon investigation found that the two sets of men were working against each other, so by starting one set in the opposite direction the span was readily put in motion. This example is given to show how ignorant workmen will abuse machinery, and the consequent necessity for making man-power apparatus extra strong, notwithstanding all the opposition that may be offered thereto by bridge manufacturers. It is thought that the method of proportioning such apparatus, which is specified in Chapter XV, [p.204-208] will develop ample strength, more especially as the specifications prohibit the use of cast-iron gears.

As a drawbridge is a piece of machinery, it will require a certain amount of care, for otherwise it will get out of order and give trouble just at the wrong time. It should be opened at least once a month, and all parts which move on other parts, especially the wheels and tracks, should be kept clean and well lubricated, The lower rolling surface for the wheels should be kept free from all obstructions, and the wheels should be maintained in proper adjustment by means of the spider-rods. The operating machinery also should receive due care and attention.