National Geographic : 1947 Mar
© National Geographic Society Ektachrome by Willard R. Culver How Much Weight from Ice-laden Wires Will Break a Crossarm on a Pole? Hydraulic Machine Gives the Answer Engineers test a crossarm to the breaking point. They use the machine to determine the strength of the various types ofwood available for crossarms. Southern pine and Douglas fir crossarms, recently tested, broke under an average load of about two tons.