To me this modification of the Laplacian hypothesis is unsatisfactory, for several reasons. To mention only one: if Jupiter was a large gaseous mass extending out as far as the 8th and 9th satellites, the gaseous body was very highly attenuated; friction in the outer strata would be essentially a negligible quantity, and tidal retardation would not be very effective; and it would be under just these conditions that loss of heat from the planet should be most rapid and the rate of increase of retrograde rotation resulting therefrom be comparatively high. It would seem that the rotation of the planet in the retrograde direction must have accelerated under the contractional cause, rather than have decreased and reversed in direction under an excessively feeble tidal cause. The recognized weaknesses of Laplace's hypothesis have caused many other hypotheses to be proposed in the past half century. The hypotheses of Faye, Lockyer, du Ligondes, See, Arrhenius, and Chamberlin and Moulton include many of the features of Kant's or Laplace's hypotheses, but all of them advance and develop other ideas. It is unfortunate that space limits do not permit us to discuss the new features of each hypothesis. (To be continued.) PROGRESS AND PEACE BY PROFESSOR ROBERT M. YERKES HARVARD UNIVERSITY LASTING peace among the nations of the earth we must regard as of supreme moment, the discovery of the conditions thereof, as most worthy of human effort. Physical struggle is no longer accepted as either a necessary or a desirable means of settling differences between individuals. Why, then, should it be tolerated to-day in connection with national disagreements? To admit the impossibility or the impracticability of universal peace is to stigmatize our vaunted civilization as a failure. Surely we will not, can not, humble ourselves by such an admission until we have exhausted our energies in searching for the conditions of national amity. With my whole life I believe in the possibility and value of worldwide friendliness and cooperation. I am writing to discuss not the attainability or the merits of peace, but ways of achieving it; not to criticize present activities on its behalf, but to indicate the promise of a neglected approach and to present a program which should, I believe, find its place in the great "peace movement." Must peace be achieved and maintained by brute strength, regardless of sense and sentiment, or may it be gained through intelligence, humanely used? Must the pathway thereto be paved with human skulls, builded with infinite suffering and sacrifice, or may it he charted by scientific inquiry and builded by the joyous labor of mutual service and helpfulness? Is it possible, in the light of the history of the races of man, to doubt that we must place our dependence on intelligence sympathetically employed, not on physical prowess? To me it seems that peace must be achieved peacefully, not by the clash of arms and bloodshed.