THE RESOLVABLE NEBULÆ, STAR-CLUSTERS AND GALAXIES. When we come to consider the nebulæ, and endeavor to learn what part electricity has to play in the phenomena presented by these singular objects, we must recollect, in order to give them their due importance, that they are neither few in number nor uniform in constitution. Of the nebulæ, Professor Proctor ("Star-Clouds and Star-Mist") says, "When the depths of the heavens are explored with a powerful telescope a number of strange cloud-like objects are brought into view. It is startling to consider that if the eye of man suddenly acquired the light-gathering power of a large telescope, and if at the same time all the single stars disappeared, we should see on the celestial vault a display of the mysterious objects called nebulæ or star-clouds exceeding in number all the stars which can now be seen on the darkest night in winter. The whole sky would seem mottled with these singular objects." As telescopes, with the advances of constructive art, increased in power, these luminous clouds became more and more clearly defined, and many of them became resolved into clusters of stars, galaxies of suns like the Milky Way, of which latter our solar system is a constituent part, but more distant from us than the separately visible stars of that galaxy, and each separated from the relatively adjacent clusters by intervals of space comparable only with those which separate them from our own system. Of these glorious star-clusters, says Flammarion, in "The Wonders of the Heavens," "In the bosom of infinite space, the unfathomable depth of which we have tried to comprehend, float rich clusters of stars, each separated by immense intervals. We shall soon show that all the stars are suns like ours, shining with their own light, and foci of as many systems of worlds. Now, the stars are not scattered in all parts of space at hazard; they are grouped as the members of many families. If we compared the ocean of the heavens with the ocean of the earth, we should say that the isles which sprinkle this ocean do not rise separately in all parts of the sea, but that they are united here and there in archipelagoes more or less rich.... They are all collected in tribes, most of which count their members by millions." Says Professor Nichol, "System on system of majesty unspeakable float through the fathomless ocean of space. Our galaxy, with splendors that seem illimitable, is only a unit among unnumbered throngs; we can think of it, in comparison with creation, but as we were wont to think of one of its own stars. "Of these glorious star-clusters the same writer says, "That no one has ever seen them in a telescope of adequate power without uttering a shout of wonder." These mist-like star-clouds were successively resolved, nebula by nebula, until science settled into the belief that with telescopes of adequate power all nebulæ might be so resolved, and the capacity of telescopes to thus resolve nebulæ