1590.  When a ball is covered with a thick conducting fluid, as treacle or syrup, it is easy by inductive action to determine the wind from almost any part of it (1577.); the experiment, which before was of rather difficult performance, being rendered facile in consequence of the fluid enabling that part, which at first was feeble in its action, to rise into an exalted condition by assuming a pointed form.

1591.  To produce the current, the electric intensity must rise and continue at one spot, namely, at the origin of the current, higher than elsewhere, and then, air having a uniform and ready access, the current is produced.  If no current be allowed (1574.), then discharge may take place by brush or spark.  But whether it be by brush or spark, or wind, it seems very probable that the initial intensity or tension at which a particle of a given gaseous dielectric charges, or commences discharge, is, under the conditions before expressed, always the same (1410.).

1592.  It is not supposed that all the air which enters into motion is electrified; on the contrary, much that is not charged is carried on into the stream.  The part which is really charged may be but a small proportion of that which is ultimately set in motion (1442.).

1593.  When a drop of gum water (1584.) is made negative, it presents a larger cone than when made positive; less of the fluid is thrown off, and yet, when a ball is approached, sparks can hardly be obtained, so pointed is the cone, and so free the discharge.  A point held opposite to it did not cause the retraction of the cone to such an extent as when it was positive.  All the effects are so different from those presented by the positive cone, that I have no doubt such drops would present a very instructive method of investigating the difference of positive and negative discharge in air and other dielectrics (1480. 1501.).

1594.  That I may not be misunderstood (1587.), I must observe here that I do not consider the cones produced as the result only of the current of air or other insulating dielectric over their surface.  When the drop is of badly conducting matter, a part of the effect is due to the electrified state of the particles, and this part constitutes almost the whole when the matter is melted sealing-wax, oil of turpentine, and similar insulating bodies (1588.).  But even when the drop is of good conducting matter, as water, solutions, or mercury, though the effect above spoken of will then be insensible (1607.), still it is not the mere current of air or other dielectric which produces all the change of form; for a part is due to those attractive forces by which the charged drop, if free to move, would travel along the line of strongest induction, and not being free to move, has its form elongated until the sum of the different forces tending to produce this form is balanced by the cohesive attraction of the fluid.  The effect of the attractive forces are well shown when treacle, gum water, or syrup is used; for the long threads which spin out, at the same time that they form the axes of the currents of air, which may still be considered as determined at their points, are like flexible conductors, and show by their directions in what way the attractive forces draw them.