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 there must have been something which we may describe as a conflagration of hydrogen on a stupendous scale, and this outburst would account for the sudden increase in luminosity of the star, and also to some extent explain how so stupendous an illumination once kindled could dwindle away in so short a time as a few days. Viewed in the light of much later work, these early discoveries assume an increased significance.

If we were to choose that one of Sir William Huggins' achievements which gave the widest extension to our knowledge, I think we can hardly hesitate to select what Romney Robinson long ago called the "palmary discovery" of the spectrum of a nebula. It was here that in the most emphatic sense Sir W. Huggins broke new ground. The stars were known to be bodies more or less congenerous with our sun; and up to the time of which I am speaking, about a quarter of a century ago, nebulæ were often looked upon as clusters of stars too distant for us to perceive the rays from each individual point. In fact, with the erection of each great telescope the test of its performance was generally sought in its power to "resolve" nebulæ, as the process used to be called. It is true that many nebulæ wholly refused to disintegrate, but it was generally, though not universally, thought that, with increased power, even the most refractory nebula would exhibit itself as a mere cloud of stars. Remembering this fact, and remembering also the faintness of these mere stains of light, it may be readily believed that when Huggins first allowed one of these objects to throw its gleam on the slit of his spectroscope, he did not entertain much hope that this instrument, though so potent elsewhere, would avail to interpret such a dim object. If