Page:Popular Science Monthly Volume 25.djvu/669

Rh has been said, it is clear how seriously the small fraction of an inch of expansion could affect it. It is an application of the old law of the elbow-joint press reversed, the working pressure taking the place of the resistance. The work is done at a great disadvantage, but the power is almost limitless.

A very good instance of "sun-kink" could be seen some years ago on the wooden bridge leading from the elevated railroad station at One Hundred and Fifty-fifth Street, in this city, toward Ninth Avenue. A gas-pipe of wrought-iron was laid on the floor of the structure. As if to render it more susceptible to the rays of the sun, it was painted of dark color. On cold or cloudy days it lay in its normal position. On sunny days, the writer has frequently seen it bowed outward nearly or quite a foot out of line. The surface of the foot-planks under this part of it became worn by the daily friction. Finally, an arrangement of bends was introduced that operated as an expansion-joint, and now no bowing takes place.

Even 50° Fahr. seems a large rise in temperature. But it must be remembered that the temperature of rails, or similar objects, is affected by the radiant heat of the sun as well as by the atmospheric temperature. The latter is only the initial factor. The sun's rays could easily raise their absolute temperature above 100° Fahr.

 

T was very difficult to select, from the vast number of subjects relating to health and to education, one of which I could fitly speak to-day. On general education I could not venture to speak; and, believing that I should have to address a large and various audience, I thought it would be best to choose a subject by which I might urge one of the chief objects of this Exhibition, and one which I know that you, sir, have always had in view, namely, that the public themselves should consider, much more than they do, the utility and the means of maintaining their own health. I have, therefore, chosen the relation between the national health and work; especially as it may be shown in a few of the many examples of the quantity of work which is lost to the nation, either through sickness or through deaths occurring before the close of what may fairly be reckoned as the working-time of life. I think it may be made clear that this loss is so great, that the consideration of it should add largely to the motives by which all people may be urged to the remedy of whatever unwholesome conditions they may live in. It is a subject which is often in the minds of the real students 