Where portability is a main consideration—as for field- service—various special adaptations may be employed. The dynamo itself should be of as light a pattern as may be compatible with efficiency, and may be constructed of detach- able sections if difficulties of transport make that advisable. Driving-power may be derived from one of the traction- engines or motors now so generally employed in transport; or a special motor might readily be designed to transport the dynamo and other X-ray outfit, and also serve as driving- power for the dynamo when so required. An automobile of this description, recently designed for field service in the French army, is illustrated in Fig. 26.

A still more portable outfit may be designed for driving by horse-power, as shewn in Figs. 27A and 27B. Where men are readily available—as in the services—a pedal gear may be arranged, similar to the driving gear of a bicycle. In emergency, a serviceable drive may be obtained by supporting an actual bicycle frame, and connecting the dynamo by belt to the back wheel.

For screen-work they produce brilliant, steady illumination of a suitable tube, and are for this purpose excellent. For photography, a tube so excited requires a long exposure, but very good radiograms are produced. If such work be attempted, a tube specially made had better be employed.

Absence of reverse currents, and the improbability of over- heating, prolong the life of the tubes considerably.

As mentioned at the beginning of this chapter, the static machine is a favourite source in other countries, and in this country there is a probability of an improved form coming into favour rapidly when it is introduced, as we expect it to be shortly. At the present stage, however, it would not be profitable to do more here than refer readers to works on static electricity, where those machines are specially described and considered.

No related posts.