248 



KNOWLEDGE. 



[NOVEMBEE 1, 1898. 



Turning to the practical methods of worldng, one 

 finds that, in the main, apparatus of the same principle as 

 that used at the first stages of the work is used now. The 

 improvements and modifications have been made principally 

 in the domain of constructive detail rather than by employing 

 different methods. The induction coil method of exciting 

 the X-ray tube is still used by the majority of workers — 

 some of whom use coils giving as much as eighteen or 

 twenty-inch length sparks in air, although this by no 

 means infers that successful work has not been done or 

 cannot be done with coils of far smaller magnitude. Coils 

 giving three or four-inch sparks in air are quite sufficiently 

 large for obtaining perfect radiographs of the extremities 

 of the body, such as the hand, the ulna and radius, or the 

 tibia, while the writer has produced several good pictures 

 of the adult chest with only a three- inch spark. In general 

 hospital work and practice, however, the average size coil 

 used is an eight or ten-inch one, and with this available 

 spark length all the necessary radiographic and radioscopic 

 work is done, and pictures of most of the deep-seated hard 

 and soft tissues are obtained. For photographic work a 

 small frequency of interruption at the contact breaker is 

 best, while high frequency is more advantageous for direct 

 fluorescent screen work. The question of adapting the 

 contact breaker of a coil to give the rates of frequency 

 required under different conditions of working has, there- 

 fore, occupied much time. Mercury contact breakers of 

 difi'erent forms have been devised, and with arrangements 

 to vary the rate of frequency of the make and break. 

 Undoubtedly this form of break possesses a great advan- 

 tage over the ordinary spring form, as with it there is no 

 danger of what is known as "jamming " between the two 

 connecting surfaces, which takes place sometimes in the 

 ordinary break, and which is so fatal to the primary of 

 the induction coil. Mercury breaks, however, are trouble- 

 some to work, and the resulting vapour very poisonous, of 

 course. A great point is to have the mercury and the 

 connecting platinum point perfectly clean, and to assure 

 that the latter enters and leaves the former with a perfectly 

 vertical motion. Sparking is much decreased by so doing. 



The form of induction coil made by Apps or Apps-Newfcon 

 has probably up to the present been the most efficient 

 one in use, but it bids fair to be surpassed by a coil 

 recently patented by Mr. A. L. Davis, and which is now 

 about to be put on the market. By a special ebonite 

 disc plan for the insulation of the secondary coil, the 

 spark is considerably increased for the same amount of 

 wire. In an experimental coil there were from thirty 

 to forty sections, each about three-sixteenths of an inch 

 thick, making a total width of just over six inches. 

 With this coil, and using only three accumulators giving 

 six volts in all, a continuous thick spark of ten inches 

 was obtained. One advance with the above arrangement 

 of Insulation is that the secondary can be wound right 

 down upon the tube insulating the primary. 



When working with an induction coil great care has to 

 be taken, of course, not to pierce the insulation, as that 

 would be fatal ; moreover the recharging of the necessary 

 batteries is always a trouble unless one is near a charging 

 station, or can get over the difficulty at home, and these 

 drawbacks are increased very considerably when military 

 field work or other expedition work is being undertaken, 

 and there is no possible chance of getting things rectified 

 once they go wrong. 



The Wimshurst machine, as an exciter for X-ray tubes, 

 possesses many advantages over the coil in some respects, 

 and will probably be utilised much more in certain cases 

 and localities. That Wimshurst machines are quite 

 efficient for working X-ray tubes under all conditions 



and for all purposes has been proved by several in- 

 vestigators. Through the courtesy of Mr. Wimshurst, 

 the writer has had the opportunity of testing the capa- 

 bilities of the many sized machines in the inventor's 

 possession. These results have shown that, provided the 

 diameter of the plates is not less than twenty inches, very 

 excellent and uniform fluorescent screen illumination is 

 obtained, the rays emitted from the tube in use being 

 of good penetrating value. A tube which previously had 

 been found to be best adapted for a six-inch coil, worked 

 'admirably on a machine with four plates of twenty inches 

 diameter. Using higher resistance tubes upon larger 

 machines, and inserting in the circuit a small spark gap 

 suitable to the exhaustion of the tube (the gap varying 

 from one-half inch to one and a-half inches) much better 

 results still were obtained. Further, the work with a 

 Wimshurst machine proceeds noiselessly and without the 

 flickering in the tube so often noticed with coils. The 

 working also entails no more trouble than the mechanical 

 turning of the plates. 



At first sight the Wimshurst machine does not seem so 

 portable as the induction coil, but when one takes into 

 consideration the necessary important accessory of the 

 latter, viz. ; — the battery and the trouble it incurs — the 

 relative portability of the machine is much increased. 

 Furthermore, the Wimshurst with ebonite plates gives 

 better fluorescent screen results than glass, and ebonite 

 is practically unbreakable ; the prime conductors can 

 also be much reduced in size and capacity without 

 affecting the efiiciency for X-i-ay work. Considering, 

 then, that rapid radioscopic work upon the field of 

 battle is of much more importance than radiography, 

 there is no doubt that, so long as the minimum size 

 of plates is attained, and the machine made as compact 

 as possible, it should prove of very great value to the army 

 surgeon. 



There only remains one more important practical item 

 to be considered, namely, the vacuum tube for exciting the 

 X-Rays. In principle this remains the same as the "focus " 

 form originally introduced by Professor -Jackson, of King's 

 College, in which the cathode rays, emanating from the 

 cathode, impinge upon the anode or anti-cathode and are 

 scattered out through the glass as Rontgen rays. Two 

 difficulties, however, presented themselves. Firstly, under 

 different conditions of working and different spark lengths, 

 the one tube with its one degree of exhaustion and one 

 value of resistance could not be adapted. Secondly, upon 

 lontinued working it was found that the exhaustion and 

 therefore the penetrating value of the tube increased, so 

 that, finally, in spite of repeated heatings by a flame so as 

 to increase the pressure inside, the resistance of the tube 

 was so high that discharge could not take place under the 

 same conditions it was originally selected for. 



These difficulties have been overcome chiefly owing to 

 the persistent, patient work of Mr. A. A. C. Swinton, 

 whose results upon the modus operandi in the interior of 

 the tube and also upon the conditions affecting the 

 emission of X-rays have proved of very great importance 

 in the work. Among other things, !Mr. Swinton found, 

 with experimental tubes made in his laboratory, that if the 

 anode of the tube be so arranged that the distance between 

 it and the cathode could be adjusted, then a ready and 

 very simple means was at hand whereby the resistance 

 and penetration could be altered to suit the varied 

 conditions imposed. The nearer the anode is placed to 

 the cathode the higher the resistance and consequently the 

 higher the penetration of the tube, and liec t-ersil. In moving 

 the anode of a tube, however, the point of origin of the 

 X-rays is also moved for each adjustment, which is 



