_neg_. | _pos_. | _neg_. |
|_______________|_____________|_____________|_____________|_____________|
| | | | | |
| Air | 0.55 | 0.30 | 0.40 | 0.75 |
| Nitrogen | 0.30 | 0.40 | 0.52 | 0.41 |
| Oxygen | 0.70 | 0.30 | 0.45 | 0.82 |
| Hydrogen | 0.20 | 0.10 | | |
| Coal gas | 0.13 | 0.30 | 0.30 | 0.44 |
| Carbonic acid | 0.82 | 0.43 | 1.60 | {above 1.80;|
| | | | | had not |
| | | | | space.) |
|_______________|_____________|_____________|_____________|_____________|

1519. It is to be understood that sparks occurred at much higher intervals
than these; the table only expresses that distance beneath which all
discharge was as spark. Some curious relations of the different gases to
discharge are already discernible, but it would be useless to consider them
until illustrated by further experiments.

* * * * *

1520. I ought not to omit noticing here, that Professor Belli of Milan has
published a very valuable set of experiments on the relative dissipation of
positive and negative electricity in the air[A]; he finds the latter far
more ready, in this respect, than the former.

[A] Bibliotheque Universelle, 1836, September, p. 152.

1521. I made some experiments of a similar kind, but with sustained high
charges; the results were less striking than those of Signore Belli, and I
did not consider them as satisfactory. I may be allowed to mention, in
connexion with the subject, an interfering effect which embarrassed me for
a long time. When I threw positive electricity from a given point into the
air, a certain intensity was indicated by an electrometer on the conductor
connected with the point, but as the operation continued this intensity
rose several degrees; then making the conductor negative with the same
point attached to it, and all other things remaining the same, a certain
degree of tension was observed in the first instance, which also gradually
rose as the operation proceeded. Returning the conductor to the positive
state, the tension was at first low, but rose as before; and so also when
again made negat