PRODUCED IN GASES BY RONTGEN RAYS. 
231 
velocities here obtained the inclination would be somewhat less. The final values 
thus obtained for hydrogen saturated with aqueous vapour when corrected for the air 
present give for the velocity of the negative ions 5‘6 centims. per second, and for the 
positive ions 5'3 centims. per second at a pressure of 76 centims., and a temperature 
of 20° C. 
§ 12. Remarks on the Experiments. 
The changes in the values obtained for the velocity with changes of T are 
observed to be greater for those cases where the ionic velocities are higher. 
With dry and moist carbonic acid, however, the inclination of the curves is some¬ 
what different for nearly equal values of the velocities. In some instances, where 
the set of points for either the positive or the negative ions did not allow of a 
sufficiently accurate estimate of the inclination of the line to be drawn through them, 
the line through the other set of points was used as a guide. 
The presence of water vapour diminished the velocity of the negative ions in all of 
the gases, while in carbonic acid the velocity of the positive ions was at the same 
time considerably increased. It seems most probable that these changes are due to 
some effect upon the size of the ions, and it is possible that a few molecules of the 
aqueous vapour collect upon the negative ions. It is interesting to note in this con¬ 
nection the recent results of C. T. II. Wilson,^ showing that in supersaturated air 
the water condenses more readily upon the negatively charged ions. 
While in most cases the readings indicate a greater accuracy, it is believed that 
the maximum error in any determination is less than five per cent. For convenience, 
all of the values obtained are here collected in one table, the results being given in 
centims. per second both for a field of one volt per centim. and for a field of one 
electrostatic unit per centim. 
Table XXII.—Ionic Velocities. 
* 
Velocities in centims. 
Velocities 
. 
in centims. 
per second in a field of 
per second in a field of 
Ratio 
Gas. 
1 volt per centim. 
1 E.S.U. per centim. 
of 
Negative 
Tempera- 
" ture. 
to 
Positive 
Negative 
Positive 
Negative 
Positive. 
ions. 
ions. 
ions. 
ions. 
Air, dry. 
1-36 
1-87 
408 
561 
1-375 
°C. 
13-5 
„ unoist. 
1-37 
1-51 
411 
453 
1 TO 
14 
Oxygen, dry .... 
1-36 
1-80 
408 
540 
1-32 
17 
,, moist . 
1-29 
1-52 
387 
456 
1-18 
16 
Carbonic acid, dry . . 
•76 
•81 
228 
243 
1-07 
17-5 
,, „ moist . 
■82 
•75 
246 
225 
•915 
17 
Hydrogen, dry . 
6-70 
7-95 
2010 
2385 
1T9 
20 
„ moist . . 
5-30 
5-60 
1590 
1680 
1-05 
20 
* C. T. R. Wilson, ‘Phil. Trans./ A, vol. 193, p. 289, 1899. 
