a structure due to the action of water. It is readily guarded against at small cost; hence, for aesthetic as well as preservative reasons, water-proofing is well worth while.

This consideration, apparently purely aesthetic, has, paradoxical as it is may seem, a distinct place in a discussion of the economics of bridge water-proofing. Cities and towns are in constant competition with each other for new industries. Large sums of money are spent annually by these municipalities or their Boards of Trade in advertising their advantages as loci for manufacturing enterprises. Visible evidences of a spirit of progress in the community, obvious care in attention to details of appearances of public structures, are impressive and cannot fail to attract the notice of prospective residents. This makes for the wealth and progress of all concerned. When a visitor's first impression of a city is produced by seeing what should be a beautiful monumental construction covered with the disfiguring surface-blemishes which water-penetration produces, he is apt to turn to a competitor whose neglect of detail is not so marked; for to the layman-this term being used to differentiate from the engineer—such blemishes mean more than mere surface disfiguration, because they convey the impression of general disintegration and eventual failure, and reflect unfavorably upon the community or the owner of the structure.

It is not contended that the neglect to water-proof a concrete bridge will always result in its ultimate destruction. Many bridges which are not water-proofed are still intact; few have completely failed. But water-proofing certainly does provide a measure of protection. It is, in fact, a form of insurance. The cost is small not more than two per cent of the total-so that if it extends the life of a bridge only a year or two, it is worth while, since the prolonged use of the structure is almost always of greater value than the extra cost plus compound interest thereon. When, however, the protection afforded is not merely for a year or two, but for a great many years, the life of the water-proofing being the only limit, and even that being capable of extension by renewals, it is obvious that the additional cost incident thereto is a wise investment.

Although, of late years, the author has been specifying the addition of a small percentage of hydrated lime to the cement used for making concrete in bridgework, with the dual purpose in view of increasing fluidity and reducing porosity, he has not called for blanket water-proofing and flashing, excepting where there was special reason for preventing drip; but, because of the convincing character of the preceding dissertation, he has decided that in future, if his clients can be persuaded to stand for the additional expense, he will adopt every available effective means in order to water-proof his structures thoroughly.

Since the preceding was written, the author's attention has been called to an important paper delivered to the Brooklyn Engineers' Club in May,