545 
lEtO'NTG-JSN EATS UP-TO-DATE. 
pud cis 
Of a Lecture delivered at the Royal Artillery '.Institution, Woolwich,^27th} January, 1898. 
- BY — 
W. WEBSTER, ESQ., F.C.S. 
THE lecturer, after mentioning the great improvement in controlling 
the X Rays since his lecture of 1896, went on to state that Professor 
Jackson, of Kings' College, had invented his focus tube in 1894, 
nearly two years before Professor Rontgen's crowning observation; 
Jackson also worked with a phosphorescent screen, but confined his 
experiments to material objects such as leather, wood, vulcanite and 
metals. Mr. Webster then exhibited Jackson's original tube, showing 
there was no absolute difference in the form as now used all over the 
world; the tubes being an improved form of Crooke's tube, whose 
work in electric discharge in high vacuo led up to the discovery of the 
properties of the X Rays. A 20-inch induction coil made by Messrs. 
Newton and Apps was then exhibited in action, giving a 20-in. con- 
tinous spark between the dischargers, it was explained that a 10-in. 
coil of the same make would produce similar results as the 20-in. in 
vacuo, but that the high vacuum tubes required rendered it necessary 
to work the 10-in. coil ab its highest capacity, whereas with the 20-in. 
coil forcing was not necessary and there was less sparking at the 
make-and-break. Special mention was made of the perfect working 
of the Apps' make-and-break. 
The focus tube having been attached to the dischargers of coil, a 
practical demonstration of conditioning the tube by heating behind 
the cathode was given; by this heating the phosphorescent discharge 
in vacuo showed the violet colouration behind the anode when the 
anode was red hot with an almost white hot spot where the discharge 
impinged at the focal point, ultimately the violet gradually disappeared 
leaving the phosphorescence a yellow-green tint. Ab this point 
shadows of hands and arms can be photographed in from a fraction of a 
second to five or six seconds. The trunk of a child showing ribs, 
heart, etc., can be taken in 30 seconds or even less ; the adult trunk 
in two or three minutes. Prints of photographs illustrating these 
results were handed to the audience. 
Vacuum tubes showing different degrees of exhaustion were then 
ii. vol. xxv, 4 7 
