this is practicable. When exact analysis is impossible, an ample amount of metal should be used so as to avoid any possible weakness due to such uncertainty; but this does not mean that it is well to be recklessly extravagant of metal in order to save the trouble of figuring the strength.

It is false economy of the worst type to skimp details; because the saving in metal is comparatively small, and the loss of strength may be very great. It is worse than useless to adopt low unit stresses for the main members and put in weak details; for the stress sheet then gives a false sense of security. It would be much better to have strong details and high working stresses in the main members.

Details and joints frequently defy exact analysis; and in such cases the designer should not fail to make approximate analyses to determine the character and magnitude of stress in every part so as to avoid all possibility of the existence of weak spots. It is not unusual to see metal placed at a joint where it could not possibly do any good, while an important component part of a member is left unspliced. A ten per cent error in strength on the side of danger will rarely do any harm; but the complete omission of a vital part of a detail may be very serious. For instance, in the lateral systems of highway bridges, it is not uncommon to see a diagonal of strong section connected by details so flimsy that they could not possibly transmit one-quarter of the stress which the said diagonal is capable of withstanding. The metal in such a lateral system is nearly all wasted.

As an important matter of economy, rusting and other kinds of deterioration should be carefully considered when making designs. It is very uneconomical to use parts which will rust out or wear out in a small fraction of the possible life of the structure. Repairs are not only expensive per se, but also they generally interfere seriously with the traffic. Some important railroads use 7/16 inch or even 1/2 inch as the minimum thickness of metal in steel superstructures; because they find thin metal to be one of the most fruitful causes of replacement. The author, however, is of the opinion that, if the said companies were to adhere to the 3/8 inch minimum thickness and keep the metal always properly painted, they would obtain more satisfactory results.

All parts should be easily accessible to the paint brush; for otherwise the painters will fail to cover some metal that is difficult to reach, thus curtailing the life of the structure. A horizontal plate in a bottom chord will frequently save metal; but it invites rusting, and therefore is sure ultimately to prove uneconomical.

When there is a choice of plates and shapes that can be used in the makeup of a member, it is sometimes practicable to economize a little by adopting the most inexpensive ones; but too often it will be found that the more expensive shapes are also the ones which are the more appropriate and serviceable.