1505.  With respect to the general condition and relations of the positive and negative brushes in dense or rare air, or in other media and gases, if they are produced at different times and places they are of course independent of each other.  But when they are produced from opposed ends or balls at the same time, in the same vessel of gas (1470. 1477.), they are frequently related; and circumstances may be so arranged that they shall be isochronous, occurring in equal numbers in equal times; or shall occur in multiples, i.e. with two or three negatives to one positive; or shall alternate, or be quite irregular.  All these variations I have witnessed; and when it is considered that the air in the vessel, and also the glass of the vessel, can take a momentary charge, it is easy to comprehend their general nature and cause.

* * * * *

1506.  Similar experiments to those in air (1485. 1493.) were made in different gases, the results of which I will describe as briefly as possible.  The apparatus is represented fig. 131, consisting of a bell-glass eleven inches in diameter at the widest part, and ten and a half inches high up to the bottom of the neck.  The balls are lettered, as in fig. 130, and are in the same relation to each other; but A and B were on separate sliding wires, which, however, were generally joined by a cross wire, w, above, and that connected with the brass conductor, which received its positive or negative charge from the machine.  The rods of A and B were graduated at the part moving through the stuffing-box, so that the application of a diagonal scale applied there, told what was the distance between these balls and those beneath them.  As to the position of the balls in the jar, and their relation to each other, C and D were three and a quarter inches apart, their height above the pump plate five inches, and the distance between any of the balls and the glass of the jar one inch and three quarters at least, and generally more.  The balls A and D were two inches in diameter, as before (1493.); the balls B and C only 0.15 of an inch in diameter.

Another apparatus was occasionally used in connection with that just described, being an open discharger (fig. 132.), by which a comparison of the discharge in air and that in gases could be obtained.  The balls E and F, each 0.6 of an inch in diameter, were connected with sliding rods and other balls, and were insulated.  When used for comparison, the brass conductor was associated at the same time with the balls A and B of figure 131 and ball E of this apparatus (fig. 132.); whilst the balls C, D and F were connected with the discharging train.