In the great spiral nebula in the constellation Canes Venatici (see illustration in Chapter XII.) we perceive that the tail of the smaller nebula has been drawn into the outer convolution of the great spiral, against the radial repulsion of the latter nebula, as we can see by its curvature. This can only be due to a tremendous inflowing current in space. Were the deflection due to gravity the trend would be to the center and not to the outer convolution of the larger nebula. Professor Nichol says, "The spiral figure is characteristic of an extensive class of galaxies." Not only in the spiral, but in other forms of nebulæ we may observe these currents of space, so that we cannot fail to perceive that they exist, and we should even conclude, a priori, that these must exist. In the elongated linear nebula in Sobieski's Crown, illustrated above, its length is deflected into irregular curves apparently due to counter-currents of space. These gaseous nebulæ, Flammarion says, "appear like immense vaporous clouds tossed about by some rough winds, pierced with deep rents, and broken in jagged portions." It may be said generally that every sun, as it drifts through space, must leave a wake of increased electric potential among the molecules which line its pathway. Beyond the limits of every vortex extend radial or tangential, polar or equatorial, streams of space, and these must extend without limit until deflected or neutralized by other conditions. Throughout all space, just as in our own atmosphere, but vastly more slowly, there must be an infinitude of movements in every direction,--movements in lines, circles, vortices, ellipses and irregular curvatures, and of all possible varieties of mass and volume.