60 THE POPULAR SCIENCE MONTHLY. 



spectroscope could tell us the nature of the substances to the combus- 

 tion of which the light is due, and even the conditions of temperature 

 and of pressure under which the combustion is taking place ; but it 

 could not disentangle those parts of the phenomenon which are due to 

 direct, from those which are due to reflected or to scattered light. It 

 was for the polariscope to tell us whether the corona is a terrestrial 

 effect a mere glare, in fact, from our own atmosphere or a true solar 

 phenomenon ; and in the latter issue, whether any of it is due to direct 

 rays from incandescent matter, or all of it to rays originating in such 

 incandescent matter below, but scattered laterally from gases which 

 have cooled in the upper regions surrounding the sun. This question 

 has not even yet received a definitive answer. But the brief account 

 given within the last few days by Mr. Lockyer, in anticipation of his 

 more complete digest of the voluminous reports from the various 

 branches of the Expedition, seems to justify us in the conclusion that 

 the corona is substantially a solar phenomenon due not to direct but 

 to reflected or scattered rays. 



The principle upon which the polariscope enables us to make these 

 refined distinctions in such far-off phenomena is, after all, very simple. 

 If the corona were due wholly to the effect of our atmosphere on such 

 light as reaches us during a total eclipse of the sun, the whole of that 

 light would be similarly affected, because it comes very nearly from 

 the same part of the heavens. In other words, its polarization would 

 be uniform, and the corona, when examined by a Nicol and quartz, 

 would appear of a uniform color. But if the phenomenon were wholly 

 due to the sun and its surroundings, the light would be affected, if at 

 all, differently in different directions drawn outward (like spokes or 

 radii of a wheel) from the sun as a centre. In other words, its polari- 

 zation would be arranged spokewise, or, to use the technical term, 

 radially; and the corona, when examined as before, would vary in 

 color on different sides of the sun. 



I have already drawn largely, perhaps too largely, upon your 

 patience. But it will not have been without purpose that, besides 

 witnessing the exhibition of a few experiments, you should have seen, 

 at least in outline, what manner of thing a scientific investigation is. 

 "Well, whatever it is (and I will not weary you with a dry statement 

 of its processes), the foundation of it must always be laid in careful, 

 accurate, and intelligent observation of facts. And it is a considera- 

 tion which may well stir the hearts of us outsiders of science, especially 

 on an occasion when we come face to face with some of the greatest 

 philosophers of our time, that any one of us, by practising his eye and 

 riveting his attention, may contribute some natural fact, some fragment 

 of knowledge, to the common stock. And surely has not this a particu- 

 lar significance and importance to us, at a period when, by shortening 

 the hours of labor, more leisure, as we may hope, will be at the com- 

 mand of many? It will, I take it, be our own fault if we spend that 



