DISRUPTIVE DISCHARGE — POSITIVE AND NEGATIVE DISCHARGE IN GASES. 133 



some gases, as in carbonic acid gas and coal gas (1399.), whilst in others that con- 

 clusion seems more doubtful ; and in others, again, there seems a probability that 

 the positive small ball may be superior. All these results were obtained at very 

 nearly the same pressure of the atmosphere. 



1518. I made some experiments in these gases whilst in the air jar (fig. 17-), as to 

 the change from spark to brush, analogous to those in the open air already described 

 (1486. 1487.). I will give, in a Table, the results as to when brush began to appear 

 mingled with the spark ; but the after results were so varied, and the nature of the 

 discharge in different gases so different, that to insert the results obtained without 

 further investigation, would be of little use. At intervals less than those expressed 

 the discharge was always by spark. 



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 pub- 

 lished a very valuable set of experiments on the relative dissipation of positive and 

 negative electricity in the air*; he finds the latter far more ready, in this respect, 

 than the former. 



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 connection with the subject, an in- 

 terfering effect which embarrassed me for a long time. When I threw positive elec- 

 tricity from a given point into the air, a certain intensity was indicated by an elec- 

 trometer 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 opera- 

 tion proceeded. Returning the conductor to the positive state, the tension was at 

 first low, but rose as before ; and so also when again made negative. 



♦ Bibliotheque Universelle, 1836, September, p. 152. 



