of lead, and measurements of the coefficient of absorption λ were made for additional thicknesses. The average value of λ was calculated from the usual equation
where d is the thickness of matter traversed. The following table shows the value of λ, (I) for the first 2·5 mms. of matter traversed (after initially passing through 8 mms. of lead), (II) for the thickness 2·5 to 5 mms., (III) for 5 to 10 mms., (IV) 10 to 15 mms.
TABLE A.
| Substance | I | II | III | IV |
|---|---|---|---|---|
| Platinum | 1·167 | |||
| Mercury | ·726 | ·661 | ·538 | ·493 |
| Lead | ·641 | ·563 | ·480 | ·440 |
| Zinc | ·282 | ·266 | ·248 | ·266 |
| Aluminium | ·104 | ·104 | ·104 | ·104 |
| Glass | ·087 | ·087 | ·087 | ·087 |
| Water | ·034 | ·034 | ·034 | ·034 |
In the above table, the absorption in aluminium, glass and water was too small to determine