| 
; 
‘ 
i 
‘caused by the B and y Rays of Radium. 671 
The liquids were poured into a tray beneath the blocks, and 
the secondary rays, passing obliquely upwards, were measured 
by the electroscope. Plates of various solid substances were 
substituted for the liquids, and the magnitudes of the secondary 
radiations from the liquids were interpolated from the known 
values of the radiations from the solids. 
The rate of collapse of the gold leaf of the electroscope was 
measured by a microscope with a micrometer eyepiece. 
Results.—The secondary radiation, when air is the radiator, 
is very small. The number of scale-divisions indicated by the 
electroscope, due to natural leak, to penetrating y rays, and 
to secondary radiation from air and surrounding bodies, was 
subtracted from the number of scale-divisions when a thick 
lead plate was used as radiator. This difference was taken 
as a measure of the secondary radiation from lead due to the 
8 and y rays of radium. An aluminium screen *85 mm. 
thick, or a brass screen ‘04 mm. thick, was then placed in 
front of the electroscope in order to measure the absorption 
of the secondary rays; and similar measurements were made 
for various secondary radiators. 
The following table gives the results in scale-divisions per 
TaBLE |.— and y¥ rays. 
| | / 
| | Sec. Rad. ‘Aluminium) Brass 
Radiator. | Density. “Radiation, Density. | wane cm. | i em. | 
—$ 
Mercury °......| 13°6 ree tes 10°8 ) 
a | 14 141 BDA NO AE aes ae 
Copper ......... | os havea 90. jy 20 ae eOe "ae 
Ee... ee ae eb iy OG"! 1) 62a iyi 
Iron (wrought) 78 | 75 9°6 20 lig, | 
Bie ....... v4 | 73 99 20°3 
Dye aaa 70 79 Peis 
Gramite ..2...... 2D bas eee ae 200 124 
BeapG 2. 2.2....... 2°6 | 53 | 204 121 89 
Aluminium 26 ) 42 Neer LOL 24 114 
les... es Mane hee = 176 ee a ee 
Cement ......... DAF ome We wit. 196 135 | 
Jel Ce 2-2 49 | 22:3 13:0 78 
Ebonite......... id 32 | 291 26 168 
Water’ .:....... 10 24 | 240 21 173 
ee gee, 26 fe eer | 
Pease. 9 9 * si a7.) 188 21 cs | 
» liquid.| Sb | 16 | 188 ) | 
Mahogany...... “OD. | 214 | 382 23 | 164 
2 . at AO | 52 22 113 
Millboard ...... ri) 1F4y) | 48 | . 20% 147 
Papier-maché . a / 219 | / 
Basswood ...... “aGe.- -.| Wy | Ot bn 147 
A oo 2 Bae cc cee | 21°8 2 21 boas 
X-ray screen...| oe | a: hee ee | | 
Ba: Wy 
