198 
RONTGrEN RAYS. 
known as the Geissler tube. The Geissler tubes are simply vacuum 
tubes. When the study of electricity in a vacuum first became necessary 
for the lecturer, these tubes (on the screen) were manufactured in 
Germany, and I am bound to say that although I have had them now 
close upon 25 years, they are as good as they were the day I bought 
them, and are therefore somewhat precious, as I have never found 
others quite so good. Perhaps it is that old associations always make 
one think that in the days when one was younger things seemed very 
much better. 
I have seen some very beautiful tubes, but have never seen any 
prettier than these are. (The lecturer experimented in the dark). (Loud 
applause). While that is going on, for the benefit of those at the side 
who cannot see, I have here another vacuum tube of a different make 
and a different shape, and I will allow the discharge to pass through my 
fingers from the tube. (Exhibiting the same). Now those different 
colours that you see are due to gases of different kinds in a very 
attenuated form, probably the 300th of an atmosphere. 
The first tube contains a trace of phosphoretted-hydrogen ; here we 
have hydrogen only. There you have an attenuated atmosphere of 
oxygen, and here you have hydrogen and oxygen, in a double division. 
You notice that instead of there being the yellow or pink spark or yolk 
of the Electric Egg, we have here lustrous striae discharging from one 
pole to the other, positive to negative ; and notice that the poles of this 
bottom tube change colour on altering switch. 
I do not know whether it is dark enough for you to notice, on switch¬ 
ing off the current, the phosphorescence in the top and bottom tubes 
and the summer lightning, as I call it, which you see flickering. 
(Applause). All this is very pretty and very interesting, but beyond 
being an illustration of a discharge of electricity in a certain vacuum, it 
is of no utility. 
Now we come to the Focus tube, and here is an interesting little fact 
which perhaps may be of some importance in the history of the evolu¬ 
tion of this process. Sir Benjamin Richardson in 1868 read a paper 
before the British Association at Norwich, and exhibited a lamp con¬ 
structed so as to show the transmission of light through the structure of 
animals’ bodies ; and he really repeated the experiments of the great 
Priestly, who showed that, on passing a discharge through the fingers 
from a Leyden jar, their structure became luminous in the dark. The 
bones of a child’s arm, as shown by Richardson in 1868, could be 
distinctly seen by means of subdued light ; also in very thin children 
the outlines of the heart and the ribs could be seen. Of course I was 
not there to see them, but there is no doubt that it took place ! But 
that was a very different thing from the X Rays, being really incan¬ 
descence of a sort, and without the peculiar luminous effect that we get 
by means of these rays ; in fact, I shall show that the rays have no 
colour, you cannot see them ; and then I will show you by means of a 
screen, made of cardboard coated with potassium platino-cyanide, that 
these rays have the power of making this particular chemical substance 
phosphorescent. 
This is the Jackson tube of high vacuum that produces these peculiar 
effects. It consists of a thin glass globe with a tube at each end ; to the 
ends of tubes are welded the fine platinum wire terminals, the wire at 
one end being attached inside tube to the anode platinum reflector of 
thin foil left side of globe ; and at the other to the concave cathode 
