Simon Newcomb

“ The accompanying figure shows the form of the outline, as it would appear to an observer on an outer planet were the light of the sun cut off. The hypothesis which best explains all the phenomena is that the light is that of the sun reflected from an extremely tenuous cloud of particles having the form and extent described, and becoming more and more tenuous as the earth’s orbit is approached until, immediately outside the orbit, it fades into complete invisibility. The fact that the light widens out toward the sun leads to the inference that it entirely surrounds the sun. ”

“ It is therefore of interest to test this inference by observations at midnight in such a latitude that the distance of the sun below the horizon is no more than necessary to preclude the possibility of twilight. Such an opportunity is offered when the sun is near the summer solstice, in latitudes not differing much from 50° north. A transparent atmosphere and clear horizon are necessary, conditions which can best be secured on a mountain top. ”

“ Yet more divergent are the conclusions of Francis J. Bayldon, R.N.R., who made many observations while on voyages through the Pacific Ocean between Australia and the west coast of North America. He places the ascending node at the vernal equinox, and assigns an inclination of 4°. He found that as the observer moved to the north or south the axis of the light appeared to be displaced in the direction of the motion, which is the opposite of the effect due to parallax, but in the same sense as the effect of the greater atmospheric absorption of the light on the side nearest the horizon. ”

“ The result is that the light can be only indistinctly seen when the angle with the horizon is less than 45°, unless in a region where the atmosphere is unusually clear. From this statement of the conditions it will be seen that the tropical zone is the most favourable for observation, and that the most favourable hour of the day at which the light can be seen must always be the earliest after sunset and the last before sunrise. ”

“ It seems not unlikely that the final conclusion will be that instead of the reflecting matter being composed of solid particles it is an exceedingly tenuous gaseous envelope surrounding the sun and revolving on an axis the mean position of which is between that of the sun’s equator and that of the invariable plane of the solar system. ”

“ Upsala, however, is a place where the auroral spectrum can often be observed in the sky, even when no aurora is visible, and it has generally been believed that what Ångström really saw was an auroral and not a zodiacal spectrum. ”