determinations of the
velocities of the ions are given in the following table. The
velocities are in centimetres per second under an electric force of
one volt per centimetre, the pressure of the gas being 1 atmosphere.
V+ denotes the velocity of the positive ion, V- that of the negative.
V is the mean velocity of the positive and negative ions.

_Velocities of Ions.--Ions produced by Rontgen Rays._

+----------------------+------+------+------+-----------------+
| Gas. | V+. | V-. | V. | Observer. |
+----------------------+------+------+------+-----------------+
| Air | .. | .. | 1.6 | Rutherford |
| Air (dry) | 1.36 | 1.87 | .. | Zeleny |
| " | 1.60 | 1.70 | .. | Langevin |
| " | 1.39 | 1.78 | .. | Phillips |
| " | 1.54 | 1.78 | .. | Wellisch |
| Air (moist) | 1.37 | 1.81 | .. | Zeleny |
| Oxygen (dry) | 1.36 | 1.80 | .. | " |
| Oxygen (moist) | 1.29 | 1.52 | .. | " |
| Carbonic acid (dry) | 0.76 | 0.81 | .. | " |
| " | 0.86 | 0.90 | .. | Langevin |
| " | 0.81 | 0.85 | .. | Wellisch |
| Carbonic acid (moist)| 0.82 | 0.75 | .. | Zeleny |
| Hydrogen (dry) | 6.70 | 7.95 | .. | " |
| Nitrogen | .. | .. | 1.6 | Rutherford |
| Sulphur dioxide | 0.44 | 0.41 | .. | Wellisch |
| Hydrochloric acid | .. | .. | 1.27 | Rutherford |
| Chlorine | .. | .. | 1.0 | " |
| Helium (dry) | 5.09 | 6.31 | .. | Franck and Pohl |
| Carbon monoxide | 1.10 | 1.14 | .. | Wellisch |
| Nitrous oxide | 0.82 | 0.90 | .. | " |
| Ammonia | 0.74 | 0.80 | .. | " |
| Aldehyde | 0.31 | 0.30 | .. | " |
| Ethyl alcohol | 0.34 | 0.27 | .. | " |
| Acetone | 0.31 | 0.29 | .. | " |
| Ethyl chloride | 0.33 | 0.31 | .. | " |
| Pentane | 0.36 | 0.35 | .. | " |
| Methyl acetate | 0.33 | 0.36 | .. | " |