We now come to a point of the greatest interest as regards the problem we are investigating. We have seen how great is the difference in the estimates of geologists and those of physicists as to the time that has elapsed during the whole development of life. But the position we have now found for the sun, in the outer portion of the central star-cluster, may afford a clue to this problem. What we require is, some mode of keeping up the sun's heat during the enormous geological periods in which we have evidence of a wonderful uniformity in the earth's temperature, and therefore in the sun's heat-emission. The great central ring-cluster with its condensed central mass, which presumably has been forming for a much longer period than our sun has been giving heat to the earth, must during all this time have been exerting a powerful attraction on the diffused matter in the spaces around it, now apparently almost void as compared with what they may have been. Some scanty remnants of that matter we see in the numerous meteoric swarms which have been drawn into our system. A position towards the outside of this central aggregation of suns would evidently be very favourable for the growth by accretion of any considerable mass. The enormous distance apart of the outer components (the outer ring) of the cluster would allow a large amount of the inflowing meteoritic matter to escape them, and the larger suns situated near the surface of the inner dense cluster would draw to themselves the greater part of this matter.[23] The various planets of our system were no doubt built up from a portion of the matter that flowed in near the plane of the ecliptic, but much of that which came from all other directions would be drawn towards the sun itself or to its neighbouring suns. Some of this would fall directly into it; other masses coming from different directions and colliding with each other would have their motion checked, and thus again fall into the sun; and so long as the matter falling in were not in too large masses, the slow additions to the sun's bulk and increase of its heat would be sufficiently gradual to be in no way prejudicial to a planet at the earth's distance. The main point I wish to suggest here is, that by far the greater portion of the matter of the whole stellar universe has, either through gravitation or in combination with electrical forces, as suggested by Mr. Whittaker, become drawn together into the vast ring-formed system of the Milky Way, which is, presumably, slowly revolving, and has thus been checked in its original inflow toward the centre of mass of the stellar universe. It has also probably drawn towards itself the adjacent portions of the scattered material in the spaces around it in all directions.