putting in suitable bracing that will decrease the vibrations and the wear, although, strictly speaking, it will not strengthen the main truss members.

This dissertation does not aim to describe all the details of repairs necessary for bridges, because usually special problems in each case are developed; but the underlying principle of economics of maintenance of bridges and similar structures is to keep a close watch on them by frequent and thorough inspection, and to repair promptly any damage that is found. The neglect of prompt attention on a structure often leads to much unnecessarily expensive work and sometimes to the development of dangerous conditions.

The joint data of Mr. Chalfant and Mr. Covell were contained in two letters from which the following extracts have been made:

The subject will be divided for convenience into three parts, viz:

A. Masonry.

B. Floors.

C. Painting.

(A) Masonry

The constant tendency of small streams to change their courses necessitates regular inspection to prevent undue scouring and cutting of the banks and approaches. Where the nature of the foundation and depth of masonry are a matter of record, the soundings and measurements can be interpreted with comparative ease, but where this knowledge is lacking, as is true in many cases, chances should not be taken. Sometimes barriers of a more or less permanent nature can be erected above the bridge in such a manner as to turn the stream back into its natural channel, or the channel itself may be changed. When this cannot be done, heavy rip-rap should be placed around the masonry in such a manner as to fill the hole and prevent further erosion. This rip-rap may be formed of rough stones from the quarry or of blocks of concrete made at the site. When concrete is used for protection, it should be in loose blocks which are free to settle, rather than in a solid mass which, in turn, may be under-scoured.

When the stream is of sufficient size to require piers in the channel, with other than rock foundations, there should be a systematic program of soundings so that the conditions of the stream-bed around the piers may be known, and so that changes may be noted. This is essential when the masonry rests on piles, but is of even greater importance when the foundation consists of a timber grillage on gravel or other hard stratum. Heavy rip-rap is a most excellent protection to piers against scouring of the bed of the stream; but, when once placed, there can be no assurance of future security. The rip-rap may be moved by ice so that the bed around the pier is again exposed to erosion.