“If this nebula is in process of development into a solar system, the indications are for a system having certain resemblances to our solar system. Our four outer planets have a combined mass 225 times as great as that of the four inner planets. Similarly in N. G. C. 7009, there is apparently a paucity of material to form planets near the nucleus and an abundance of material for planets at greater distances from the nucleus.” [Illustration: Fig. 2. Planetary nebula N.G.C. 7009 (composite drawing, from Curtis’s photographs of the nebula made with the Crossley reflecting telescope. The scale is in seconds of arc). From _Proceedings of the National Academy of Sciences of U. S. A._] Interesting observations have been presented recently also with reference to the largest among the irregular nebulæ, namely the Orion nebula. Three astronomers in Marseilles, Bourget, Fabry, and Buisson, found that parts of this nebula, in the neighbourhood of the so-called trapeze and very close to each other, moved with different velocities and that this difference might amount to 10 km. (6.2 miles) per second. The south-easterly part approaches us while the north-easterly recedes from us. Consequently a violent whirl-motion undoubtedly takes place in this region. This observation has been verified by the well-known Chicago astronomer, Frost, who employed a different method of investigation than his predecessors. He noted differences in velocity amounting to 11 km. (6.8 miles) per second between points not over two seconds of arc distant from the trapeze. If therefore we say that the irregular nebulæ on the average possess no motion, this statement does not preclude important local deviations from the rule within the nebulæ, intimating a transformation which probably leads to the concentration of the nebulous matter toward the centre of the whirl. Leaving out, to begin with, the planetary nebulæ, it appears that the original matter of the stars stands still in space, that their average velocity increases with increasing age and approaches a mean value of about 18 km. per second or roughly 1000 times the speed of the ordinary passenger train. Our Sun, in particular, moves with a velocity of 20 km. (12.4 miles) per second toward a point in the constellation Hercules 30 degrees north of the equator.