distance approximately in a geometrical progression, a result which is in agreement with the simple theory given above. The distance through which the rays pass before they are absorbed is given below for different gases.
| Gas | Distance in mms. to absorb half of radiation |
|---|---|
| Carbonic acid | 3 |
| Air | 4·3 |
| Coal-gas | 7·5 |
| Hydrogen | 16 |
The results for hydrogen are only approximate, as the absorption is small over the distance examined.
The absorption is least in hydrogen and greatest in carbonic acid, and follows the same order as the densities of the gases. In the case of air and carbonic acid, the absorption is proportional to the density, but this rule is widely departed from in the case of hydrogen. Results