The late Mr. Proctor and Prof. Young believed "that the contraction theory of the sun's heat is the true and only available theory." The theory is, of course, a sound one; but it may now be supplemented by supposing the sun to contain a certain small amount of radium. This would bring physics and geology into harmony. Proctor thought the "sun's real globe is very much smaller than the globe we see. In other words the process of contraction has gone on further than, judging from the sun's apparent size, we should suppose it to have done, and therefore represents more sun work" done in past ages. With reference to the suggestion, recently made, that a portion, at least, of the sun's heat may be due to radium, and the experiments which have been made with negative results, Mr. R. T. Strutt--the eminent physicist--has made some calculations on the subject and says, "even if all the sun's heat were due to radium, there does not appear to be the smallest possibility that the Becquerel radiation from it could ever be detected at the earth's surface."[10] The eminent Swedish physicist Arrhenius, while admitting that a large proportion of the sun's heat is due to contraction, considers that it is probably the chemical processes going on in the sun, and not the contraction which constitute the _chief_ source of the solar heat.[11] As the centre of gravity of the sun and Jupiter lies at a distance of about 460,000 miles from the sun's centre, and the sun's radius is only 433,000 miles, it follows that the centre of gravity of the sun and planet is about 27,000 miles _outside_ the sun's surface. The attractions of the other planets perpetually change the position of the centre of gravity of the solar system; but in some books on astronomy it is erroneously stated that the centre of gravity of the system is _always_ within the sun's surface. If _all_ the planets lay on the same side of the sun at the same time (as might possibly happen), then the centre of gravity of the whole system would lie considerably more than 27,000 miles outside the sun's surface. With reference to the sun's great size, Carl Snyder has well said, "It was as if in Vulcan's smithy the gods had moulded one giant ball, and the planets were but bits and small shot which had spattered off as the glowing ingot was cast and set in space. Little man on a little part of a little earth--a minor planet, a million of which might be tumbled into the shell of the central sun--was growing very small; his wars, the convulsions of a state, were losing consequence. Human endeavour, human ambitions could now scarce possess the significance they had when men could regard the earth as the central fact of the universe."[12] With reference to the late Prof. C. A. Young (U.S.A.)--a great authority on the sun--an American writer has written the following lines:--