-loft 



KNOWLEDGE. 



Decembku, 1910. 



primary circuit amounts to about six amperes. 



Such a discharge from a 12-inch coil was not 



possible ten^years ago. and more recently it could 



jffect on 



thfc 



Figure 



The lube is placed tun metres from the photographic plate against which the patient staiuls. The shadow of tl 

 heart is but very slightlj" larger than the'heart itself, and sufficiently correct for all pr.actical purposes. 



only be obtained by using a larger coil and a large as to give out 



electrolytic interrupter, consummg 

 sixtv amperes in the primary 

 circuit. Even here this discharge 

 could not be taken advantage of 

 except with the aid of valve tubes, 

 to suppress or dix'ert the enormous 

 inverse current that was an in\ari- 

 able accompaniment of such dis- 

 charges. 



The very latest type of induc- 

 tion coil for X-ray work is what 

 is known as the "single flash 

 coil." The construction of this is 

 such that a radiograph of almost 

 an\' part of the bod\- can be made 

 with a single interruption. There 

 are different ways of bringing 

 about this effect. One maker 

 makes the interrui)tii)n by means 

 of the explosion of a small 

 cartridge : another secures the 

 same end by suddenly releasing 

 a wire that is held down in 

 a vessel of mercur\' with a catch 

 and against a spring in com- 

 pression. The act of turning on 

 the current draws back the 

 catch and the wire rushes up 

 bv the action of the spring, and the circuit is broken 

 at the moment the wire leaves the mercury. 



This is the latest development of the induction 

 coil, and in all i)robabilit\- it will have a far-reaching 

 future of X-ray technique. It is not 

 unlikeh" that in future we shall 

 be regulating our exposures, not 

 h\- so man\- seconds or minutes, 

 but b\' the number of flashes or 

 interruptions. \Miat is now- 

 wanted is a means of gix'inj; an\- 

 desired number at will. and. in all 

 probabilitv, this will be achieveii 

 before ver\' long. 



While in man\' wa\s tlie current 

 Ironi a coil is probabh' tile most 

 suitable for exciting .\-ra\ tubes, 

 the presence of the large amount 

 of inverse current in the "heavy 

 discharge" coils was such a great 

 disadvantage that inventors set 

 themseh'es to devise some means 

 of producing a high tension 

 current that was unidirectional. 

 Who was the first to do this is 

 a matter of some uncertainty, but 

 the fact remains that the first 

 practical instrument fur this 

 purpose was designed by .Mr. 

 H. C. Snook of Philadelphia. In 

 this is a transformer constructed 

 on the same principles as those 

 used commercialK-. hut so motlified 

 current of anything up to one 

 from fort\- to hundred thousand \'olts or more : the current is of 



Teleradiography. 



Figure S. TreaUncnt by the X-Rays. 



The dose is measured by means nf a "ijastile" held in the tube shield, 



course an aUernating one. 

 instrument is a sx'nchronous 



Incorporatetl in the 

 rotar\- switch, which 



