Principle XXVI.

No matter how great its weight may be, every ordinary fixed span should be anchored effectively to its supports at each bearing on same.

At one end it should be anchored immovably, and at the other so as to provide for longitudinal expansion and contraction. Such anchorage prevents the dislodging of the structure by wind-pressure or by an accidental blow from a moving object.

Principle XXVII.

The bridge-designer should never forget that it is essential throughout every design to provide adequate clearance for packing, and to leave ample room for assembling members in confined spaces.

There is no more fruitful source of profanity for bridge-erectors than the neglect of this principle; and as nearly every designer has to spend a year or two in learning to allow enough clearance, it follows that bridge-erectors should be given the benefit of "extenuating circumstances" when brought to judgment for their notorious addiction to the use of strong language.

Principle XXVIII.

Although for various reasons engineers are agreed that field-riveting should be reduced to a minimum, such an opinion should not be allowed to militate against the employment of rigid lateral systems. All designs should be arranged so that the field-rivets can be driven readily.

One of the main reasons for the unsatisfactory condition of most of the elevated railroads of this country is that their designers endeavored in every possible way to avoid field-riveting, so as to keep down the cost of erection, and in so doing failed to develop the requisite amount of rigidity in the structures.