“When we note that the orbit of the great comet of 1882 almost grazes the sun’s surface, there is a natural tendency to attribute a solar origin to it. We know from the phenomena of the solar prominences that the sun is continually erupting torrents of matter with very high speeds; a speed of 270 miles per second would suffice to send the matter round the sun in a circular orbit; if it rose to 382 miles per second the orbit would be parabolic; while for any intermediate speed it would be elliptic. By combining the observed speed of ascent of the prominence matter with the speed of approach or recession that is indicated by the shift of the lines in the spectrum, we conclude that speeds of this order are quite common, so that no difficulty arises on that account. I feel rather more difficulty from the consideration that the meteoric masses that compose a comet’s head could not exist in the sun in a solid state; the heat would suffice to vaporize them. The materials would solidify in the cold of space, but as they would be under no pressure, I imagine that the resulting solid particles would be microscopically small, not of the size required to form reservoirs for a large amount of gas. All objects ejected by the sun would move in orbits that intersect the sun, except in so far as their orbits are modified by planetary action. This latter might readily be large enough to change the orbit to one just outside the sun (like those of the sun-grazing comets of 1680, 1843, 1882, etc.). However, the great majority of known comets have orbits whose least distance from the sun is so large that we cannot imagine an origin for these by simple solar eruption. “The question arises, Can the comets have existed for so long a period in view of the wastage that they undergo? According to the geologists the date of the approach of another sun to ours (as suggested in the planetesimal hypothesis) must be put at least a thousand million years ago; in such an interval, even the comets of longest period would have returned thousands of times, and I gravely doubt whether they could continue to be such compact bodies as they appear to be; I frankly admit that I have no plausible suggestion to offer for evading the difficulty; it is one of the numerous cases in astronomy (the status of the spiral nebulæ is another) in which we must be content for the present to record observed facts and suggested interpretations, leaving full understanding to come at a later date, if at all.” According to the same authority, in connection with his views on the subject, as expressed after reading the MSS. prepared for this chapter, he writes, as follows: