76 THE ROYAL SOCIETY OF CANADA 
(3) Inverted cylinders, 30 em. high, 17 em. in diameter, were 
placed in turn on the upper platform of the well known Wulf electro- 
meter. The long axial rod, about 30 em., sold with the instrument, 
was charged initially to 200 volts, and the fall of potential, due to the 
respective rays, was measured and the natural leak deducted. 
For the y rays 14 mg. of pure radium bromide in a test tube was 
placed within a lead cylinder, 6 mm. thick, between the poles of a power- 
ful electromagnet. In this way the B rays from the radium were ab- 
sorbed and the emergent 8 rays, due to the y rays passing through the 
lead cylinder, were for the most part deflected from the electroscope 
which was a metre and a half away. 
The results given below to an arbitrary scale, without and with 
the magnetic field, show the necessity of this precaution. 
No magnetic field Magnetic field. 
BD ote eae ein EL Haken 10-9 
(Gt RE aeRO res LL 7-8 7-6 
IDDN Re at See ee ae 8-0 7-6 
| Os Ween Ca ELAS NERA aes aR Age 7-6 7-5 
A Ee ER RE ee 7-1 6-3 
Cardboard is.cssstirce= oer tne 7-0 5:3 

The Rôntgen rays came from a rather hard bulb, { in air equal 
to -0004 cm-'., and it was necessary to cut down the intensity of the 
rays by a plate of lead 1.8 mm. thick placed near the bulb, which was 
six metres from the electroscope. The time of exposure was governed 
by a control electroscope. 
Experiments were also made with softer rays and the results may 
be contrasted, iron in each case taken as standard. 

Hard x thick-|Hard x thick- 

Metal Thickness Soft X Rays Hard X Rays ness x den- | ness x atomic 
| sity. | weight. 
IPDS oe ele ee smal] 1-6 195 | 780 
CUIR ENT - 54 68 82 430 2810 
ARRETE 44 121 111 345 3190 
Mer crre ees 54 100 100 393 3080 
AIRE 60 238 126 400 2080 
Cardboard Aile DR Ne 125 pe 

It was necessary to make the lead vessel fairly thick (2.1 mim.) 
in order to secure rigidity. It was three or four times as thick as the 
other vessels. The high values for zine are in part due to its relative 
thickness. 
