Nikola Tesla Articles
X-Rays, Apparatus and Methods Page 8
Journal of the Franklin Institute - March 1st, 1897
hung, well within the can, a heavy brass wheel, having stretches of insulating slate let into its periphery. A hard- rubber lid fits over the top of the can. Mounted upon this lid are two brushes, one bearing against the wheel periphery and one against the shaft; suitable springs and screws allow the brush tension to be varied. From the commercial circuit leads are brought to these two brushes, the current being first passed through the primary of the coil and a rheostat in series. Before the lid is put in place the can is filled with distilled water; ordinary hydrant water will answer, although its usual impurity soon causes the water to become dirty, besides allowing a certain amount of electrolysis during use. With distilled water the break may be run for a number of hours without change of the water and very little heating takes place. The real function of the water is not so much to drown the spark as to prevent heating, although it does, of course, also assist in quenching the spark. But a condenser is the real spark extinguisher, and this we connect around the break just as we would around an ordinary vibrating break.
The advantages of this break over all forms of vibrating break thus far known, and over other forms of rotary break, are:
(a) Convenience. — Mere throwing of a switch being all that is required to start and stop the apparatus.
(b) Noiselessness. — Only the drowsy hum of the motor being heard.
(c) Reliability. — No chance of sticking, as with vibrating breaks.
(d) Variable Rate of Break. — Secured by adjusting rheostat in base of motor.*
(e) Smooth, Unvarying Fluoroscopic Images by reason of the large number of breaks per unit of time.
Another great advantage of the rotary break is the almost perfect control which it gives over the spark length.
* We have found that the vacuum of a tube often gets into such a condition as to make the tube absolutely unworkable at a given frequency of break, whereas, a slight change of frequency immediately restores the X-radiation.
