Electric are welding has received great impetus during the past three or four years being extended rapidly in a large variety of applications in this country and abroad. While the use of arc welding is not fundamentally new, its use as a major tool in the fabrication of large machinery, large buildings and bridges is of very recent origin in the United States, and is almost in its infancy in England, Germany, France, Poland, Russia and other foreign countries. It is not the purpose of this paper, however, to deal with applications outside of the United States. Although the applications of are welding have been extended very rapidly the developments have actually been carried out along very conservative lines. These developments have been executed step by step taking the most simple applications first and then working into larger and more complicated structures. To reap the maximum economic benefits from the use of welding it is absolutely necessary for the designer to clear his mind of prejudices to previous details of designs. He must consider a given problem from a fundamental standpoint to be certain that he will develop the most simple structure which will fulfill the requirements. His design must involve as few individual pieces as possible so as to reduce the amount of welding to a minimum. To be more exact he must strike an economic balance between the cost of structural shapes and plate at 2 to 3 cents a pound against weld metal in place at $1.50 to $3.00 a pound. In other words the designer must not simply attempt exactly to replace a casting with so many pieces of steel, welded together, and duplicating the sections and sizes of the casting. Likewise the designer must not simply take an existing riveted design for a riveted structure and merely figure on the basis of replacing the rivets with their equivalent in weld metal properly disposed to carry the stresses. Either of these practices is capable of producing a structure which is perfectly safe and strong but the resulting product will usually cost as much as, if not more than the equivalent casting or riveted structure.