196 
RONTGEN RAYS. 
It is very difficult to say what anything is ! For if you take up a 
metal, I do not care what—say, lead—you can explain all its properties, 
you can say that it is called Lead, that there are Oxides, Sulphates, and 
Chlorides, and so forth, you can describe all its reactions, that it melts 
at a certain temperature, and so on, but you do not know what it is ; it 
is an element, and you cannot split up that element. And so it is with 
Electricity, our knowledge is only finite. 
Therefore with Electricity we start with the unknown, and of course, 
this being so, it is not at all astonishing that we do not know the com¬ 
position of the X or Rontgen Rays, X being the unknown quantity ; and 
I am afraid they will be called X Rays for a very long time to come. 
Now, for the purposes of this particular application of the electric 
current for the production of these Rays, the apparatus required consists 
of :—First of all, what are called accumulators. 
Most of you know what accumulators are ; they are generally known 
as secondary batteries, and consist of a series of plates made of oxide of 
lead and lead, immersed in dilute sulphuric acid contained in cells or 
jars, which are said to be charged with electricity ; they are not actually 
so charged, but a chemical action takes place by means of the electric 
currents which, conducted by leads from a dynamo to the cells of plates, 
change the oxide of the plates and simply leave them in a different 
chemical condition ; then by coupling up the cells of those plates in 
series with wires attached to terminals a reverse chemical action is 
obtained on completing the circuit, which produces the force named 
Electricity. In fact there is very little difference between a secondary 
and a primary battery, i.e., one in which you burn or dissolve metals by 
means of acid. It does not matter what you do to produce Electricity 
for Force, Light or Heat, you must have chemical action. So much for 
the secondary batteries, the best of which are by no means satisfactory. 
Then we have what is known as the Induction Coil, on which I am 
not lecturing, and will therefore content myself by saying that the 
specimen on the table is made by Mr. Apps, and is absolutely certain in 
its action ; the primary coil is of thick insulated wire wrapped round 
the core, and a secondary insulated coil of thin wire at least 10 miles 
long wrapped round the insulator of the primary ; the make and break 
to produce interrupted current is admirable in its action, having a pull 
adjuster ; at the base are the accumulators of tin-foil. The Coil gives 
a 10-inch spark with a current of 10 amperes and an E.M.F. of 8 to 10 
volts—supplied from the secondary batteries—the 10-inch spark is 
supposed to represent 70,000 volt E.M.F. ; on this point I am by no 
means certain, as it is too high a voltage to measure, and unless I pulled 
the Coil to pieces it would be impossible to estimate it theoretically. 
The history of the discovery of this particular application of 
Electricity, to produce so-called X Rays, is one of evolution ; for in the 
Royal Society’s “ Transactions and Proceedings,” for the last forty years 
there are communications from Gassiot, Pliicker, Andrews and Tait, 
Robinson, Cromwell Varley, De la Rue and Muller, Spottiswoode and 
Moulton, Grove, Crookes, Schuster, J. J. Thomson, and Fleming ; to 
these may be added Hittorf, Lenyard and Tesla, Hertz, Lennard, and 
finally Rontgen ; and the real inventor of the improved Tube that we 
now use—and get so much benefit from—Mr. Jackson, of King’s 
College. 
As you see, this is the work of Englishmen and foreigners ; but there 
are many Englishmen connected with the evolution of this discovery, 
