Page:Popular Science Monthly Volume 57.djvu/281

Rh great deal less than previous tests on small beams had indicated, and the practice of engineers and architects has since that time been completely modified through the results obtained in this and similar laboratories. In this way does the work of such a laboratory become of direct and lasting value to the arts. The central piece of apparatus of the Institute laboratory is the Emery machine, similar to the great machine at the Watertown arsenal, with a capacity of three hundred thousand pounds. But in addition to this machine there are a dozen or more other machines designed to test beams, columns, rope, wire and, in fact, materials of every kind and in every form. An interesting machine is that for testing shafts in torsion, and it is instructive to see it twist off with apparent ease a steel shaft three inches in diameter, twisting the fibers before they break till the rod resembles a barber's pole.



There are also beam-testing machines with capacities up to one hundred thousand pounds, in which not only beams but wooden trusses may be tested to the breaking point. Some of the apparatus is of great delicacy; for instance, one instrument will measure the twist of a steel shaft two and a half inches in diameter and six feet long so delicately that the effect of a twist given by one's hand is distinctly visible; scientifically speaking, it will measure an angle of twist of two seconds. There is also a machine designed for testing stone arches, having a capacity of four hundred thousand pounds and suitable for an investigation of