results obtained are given in the following table, where λ is the coefficient of absorption.
| Substance | λ | Density | λ/Density |
|---|---|---|---|
| Glass | 14·0 | 2·45 | 5·7 |
| Mica | 14·2 | 2·78 | 5·1 |
| Ebonite | 6·5 | 1·14 | 5·7 |
| Wood | 2·16 | ·40 | 5·4 |
| Cardboard | 3·7 | ·70 | 5·3 |
| Iron | 44 | 7·8 | 5·6 |
| Aluminium | 14·0 | 2·60 | 5·4 |
| Copper | 60 | 8·6 | 7·0 |
| Silver | 75 | 10·5 | 7·1 |
| Lead | 122 | 11·5 | 10·8 |
| Tin | 96 | 7·3 | 13·2 |
It will be observed that the value of the absorption constant divided by the density is very nearly the same for such different substances as glass, mica, ebonite, wood, iron and aluminium. The divergences from the law are great, however, for the other metals examined, viz. copper, silver, lead and tin. In tin the value of λ divided by the density is 2·5 times its value for iron and aluminium. These differences show that a law for the absorption of the β rays depending only on the density does not hold for all substances. With an exception in the case of tin, the value of λ divided by the density for