X-Rays, Apparatus and Methods Page 7

out of the building, as they usually must, besides throwing the entire apparatus out of use while the charging is going on, unless one have a reserve set of batteries.

The utilization of a direct commercial circuit, such as the Edison 110-volt (e.g., where such is available), is, in every way, the most convenient and satisfactory. Until Professor Roentgen's discovery, no method of operating large coils upon such a circuit had been developed. Recently, however, several methods have been brought out, notably that of the "air break," with air blast to blow out the spark, as used by Dr. Wm. J. Morton, Dr. M. I. Pupin, and others. In Fig. 4 we show a form of apparatus devised by us to accomplish this purpose. A Lundell 1/2 horse-power motor is supported upon a base with its shaft vertical. A casting, attached to the motor, supports above the latter a copper can made up of two concentric cylinders joined by a ring below, so that the shaft passes up through the inner cylinder and thus avoids the necessity of a stuffing-box. From the shaft is