SCIENCE-GOSSIP. 



231 



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 pene- 

 tration of the tube, and vice versa In moving the 

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

 X-rays is also moved for each adjustment, which 

 is certainly a disadvantage, especially when a 

 difficult radiograph, requiring a lengthy exposure, 

 is being taken. While, therefore, taking advantage 

 of Mr. Swinton's very useful principle of varying 

 the distance between anode and cathode, Dr. 

 Dawson Turner, in conjunction with the writer, 

 reversed the arrangement by making the cathode 

 movable and keeping the anode fixed. We added 

 a further modification in that the cathode is ad- 

 justed by magnetic means, so that movement may 

 easily be made without disturbing the tube at all 

 while it is in any desired position. 



This tube, as is shown in fig. 5, is so constructed 

 that the cathode in its movement slides in and out 

 of the side annex blown in the bulb, and is kept in 

 proximity to the glass throughout its movement ; 

 for it has been found that the latter has a greater 

 influence upon the resistance of the tube than mere 

 movement to and fro when the cathode is quite out 

 into the bulb space, and it affects it in the reverse 

 way : that is, the nearer the cathode is to the anode 

 the lower the resistance, and this increases again 

 as the cathode is gradually drawn back inside the . 

 annex. Fig. 5 shows an earlier pattern of this tube, 

 in which the cathode moves out into the centre 

 of the bulb space. The present form, however, is 

 arranged so that its action depends upon this 

 proximity of the cathode to the glass. The above 



and others, when working under conditions un- 

 favourable to the supply of either coal-gas or 

 oxygen. The carrying of gas-bags or cylinders 

 from place to place is always a trouble and 

 expense, sometimes resulting in the oxyhydrogen 



Fig. 5. — Adjustable Cathode X-rays Tube. 



modifications for varying the penetration of a tube 

 are an advance over the older uncertain methods 

 of potash tubes, etc. 



Portable Limelight Apparatus Independent 

 of Coal-Gas or Compressed Oxygen. 

 This apparatus, as shown in fig. 6, should 

 prove a useful one for lantern operators, lecturers, 



Fig. 6. — Portable Limelight Apparatus. 



light being substituted by the comparatively 

 unsatisfactory oil-lantern. By means of the pre- 

 sent self-contained apparatus, the two necessary 

 gases can be generated rapidly, easily, and safely 

 within five minutes after starting. In virtue, also 

 of its portability and ease of working, it is not only 

 adapted to the above conditions, but likewise com- 

 mends itself for general use. 



The construction of the apparatus is seen 

 from fig. 6, which figure, however, does not 

 include a few small but important modifications 

 recently made. The oxygen is generated by the 

 decomposition of small cylinders or cartridges, 

 which are essentially composed of potassium 

 chlorate and black oxide of manganese. These 

 cartridges are fed at intervals through a horizontal 

 metal retort, heated by a spirit-lamp placed under- 

 neath. The spent cartridges, as they are pushed 

 through, pass into a suitable receiver. The gas 

 generated as above explained, passes 

 through this cartridge-receiver into 

 the lower bellows, and is controlled 

 by a stopcock with a spring lever, 

 by means of which the gas can be 

 shut in. By pressing down the lever 

 the oxygen is forced through a valve 

 into the upper or pressure bellows. 

 It is now between two boards and sub- 

 jected to a constant pressure from a spring arrange- 

 ment controlled by a fusee, which pressure can, 

 moreover, be varied by altering the strength of the 

 spring, a ratchet-wheel and pin being provided 

 for the purpose. From the pressure-bellows the 

 oxygen passes through a stopcock, part direct to 

 the jet to be burnt as oxygen, and part to a satu- 

 rator which is supplied with gasoline. From this 



