Tests afforded by the Stars WE will now see how the views which have been put forward are borne out by the facts which are presented to us by the stars. There is no need to occupy much time, in fact reference need only be made to Dr. Huggins' paper which was communicated to the Royal Society in the course of last year, and with that paper we may compare some earlier writings. It was as early as 1864 that Dr. Huggins, who was then associated with the late Dr. Miller, called attention to the intensely strong lines of hydrogen visible in the hottest stars.2 In this paper they pointed out at the same time that other metallic lines associated with those lines of hydrogen were thin and faint. It has been already mentioned that, as we have independent evidence that these stars are hotter than our sun, we had strong grounds for believing that here we were in presence of a result brought about by a higher temperature, associated as it was with a simpler spectrum, and, therefore, presumably with simpler constituents. We need not stop now to discuss the objection which has been put forward by an ingenious person ignorant of the facts, that the broadening of these lines may not be due to an increase of temperature at all, but really to a very rapid equatorial rotation of the star. This is a fair sample of one of the classes of objections one has to meet. Of course it is at once put out of court by the fact, also stated by Dr. Huggins, that, associated with the thick lines, are excessively thin lines. Any enormous equatorial velocity of the star should have made all the lines thick, but this is not the fact. Now we have only two lines in the solar spectrum at all comparable in thickness with these hydrogen lines in the hottest stars, taking Sirius and α Lyræ as types.