T. E. Eskin
The questions confronting the beginner in the use of the Wimshurst are so many that perhaps it may be of service to put on record one's experiences, with the hope that they may be useful to others. From the time of Rontgen's great discovery, X-ray work has always been one of my hobbies. At first work was done with a coil giving a 6 in. spark nominally, but really far more. Situated far away from all electric-power stations, the difficulty of getting accumulators charged led to the abandonment of the coil. A friend and myself commenced about two years ago to make experiments with a Wimshurst that bad a pair of plates 17 in. diameter, and the results were so good that a larger machine was built. This bad six plates, 18 in. diameter, and gave great satisfaction. This was enlarged to twelve plates, and at the present moment is being rebuilt and further enlarged to twenty plates. Needless to say, the various machines have led to diverse experiences, and misfortunes as well. Perhaps it may be well at the very outset to say that with radiations from an X-ray tube excited by the Wimshurst, I have never yet seen any trouble with dermatitis. There have been cases where exposures have been given for twenty minutes every day for three weeks without the slightest ill effects-The rays which produce the mischief seem closely associated with the hot anticathode, and with a Wims-hurst the tube always remains cool. And here perhaps it will be well to say a few words about the kinds of tube.
Of the tubes in use at different times I may mention Brady and Martin's silver medal tube. This is 5 1/2 in. long by 1 1/2 in. diameter, and is fitted with a double an ticathode, the one being a simple wire at the end of the tube, the other placed 1 in. from the end and carrying the platinum reflector. This tube did excellent service with the coil and smaller Wimshurst.
Another good tube was Watson's "Penetrator," which has a concave reflector insulated, while the anti-cathode is formed by a ring between the reflector and the cathode. This gave very brilliant results, but was badly troubled with small sparks outside the tube, which were very dangerous to its life. Covering it with cotton wool somewhat helped to do away with the danger; but it broke down, the disaster oocurring at the end of the exhaust. It was re-exhausted, but after some time it broke down again without any warning, Possibly a larger bulb would have prevented this. I lost it with great regret. Other tubes were from time to time tried, but were usually of too flimsy a construction to stand very long. The tube which is undoubtedly the best for all kinds of work is the bianodic tube, and now no other kind is in use. But with static charges, and under conditions to be described hereafter, the interior glass tube which supports the anticathode carrying the heavy platinum reflector is very liable to fracture. This occurred in two tubes, and led to collapse of the reflector. Messrs. Is-enthal & Co. have, at my suggestion, grappled with the difficulty, and as I believe, satisfactoriy. The glass interior tube which carries the reflector is blown into a bulb, which fills the recess and entirely prevents collapse of the anticathode, even if a fracture should occur. The difficulty has thus been got over simply and ingeniously and with great credit to them.
A few words may be said about the working of tubes. In contradistinction to the use with a coil, the tube when used with a Wimshurst does not rapidly run up. During a long run, say twenty minutes, it is quite clear that the penetrating power has increased; but there is none of the sticking and flickering which is so tiresome with a coil, and a tube which once works rarely requires warming or doctoring in any way. Occasionally a new tube requires coaxing at first. Because a new tube will not immediately light up it does not follow that it is too high; a quite low tube will sometimes behave in the same way. It would almost seem as if the molecules of glass had to become accustomed to a certain plane of vibration; sometimes merely wiping it will set it off, at others a careful and judicious warming and, best of all, wrapping it up as far as the cathode in cotton wool. After a time this may be removed and the tube henceforth continue to work well. It may be noted that as a tube does not appreciably run up with the Wimshurst, one which is at all blue will never be got to work satisfactorily.
In close relation to the tube is the subject of the stand for it. It requires to be firm and strong and free from vibration and so constructed that the tube can is easily reversed. The following description of a tube-stand may be useful. A, Fig. 1, is a large piece of wood to stand on the floor, carrying an upright post, AB, into which CD slides, and can be clamped to any height by the clamp E. D is a small block of wood into which a stout piece of glass rod or tubing 3/8 in. thickness is firmly inserted. On this a piece of glass tubing, HH slides freely. This passes through a piece of wood II at Fig. 2, which is 10 x 2 1/2 x 1 in. Immediately below is a second piece somewhat smaller, divided into two. Through this the tube passes at T, and by the two wooden screws SS it is held firmly in its place. The upper and lower pieces of wood are connected by four stout strips of ebonite, 7 in. long, two of which are shown at J. The top and bottom of the aperture Tis padded, and the tube can easily be turned round so that the anticathode can point either up, down or side-ways. The carrier HH allows it to be moved over the patient to the required spot, while the necessary height is regulated by the clamp at E. Should it be necessary to reverse the tube, the connecting wires are unhooked and the carrier HH put on the other way, which can be done almost instantty. The stand being on the floor, is much freer from vibration, and the connections are all out of the way. Further, the insulation is perfect and no loss of electricity is sustained, and the tube is out of danger. - "English Mechanic."