Newcomb and Young who have estimated that the visible stars are fifty to one hundred millions in number. Assuming the average mass of these stars to be equal to the mass of our sun, the amount of mass in the visible universe is about 2 X 10 metric tons. Now, if these thousand million suns had been uniformly distributed within the sphere in question, and had started from rest twenty-five million years ago, they would have acquired under the law of gravitation about such velocities as the stars are now observed to possess; or, if thousands of millions of years ago they started from rest at mutual distances asunder, very great in comparison with the radius of the supposed sphere, and so distributed that they would now be temporarily equally spaced in that sphere, their mean velocities would be of the same order

as that actually observed. A non-uni

form initial distribution of the suns

would give higher velocities for the stars than the observed values; and any great increase in the assumed number of suns would require far greater velocities than the observed values. Hence Kelvin infers that the amount of mass in our universe is greater than one hundred million times and less than two thousand million times our sun's mass.

little greater than the distance of the nearest fixed stars from our solar system.

SCIENTIFIC ITEMS.

THE great Nobel prizes, each of the value of about $40,000, have now been awarded for the first time as follows: In Medicine to Professor Behring, in physics to Professor Röntgen, in chemistry to Professor van't Hoff. The prize for the promotion of peace has been divided between Dr. Dumant and M. Passy, and the prize in literature has been awarded to M. Prudhomme.

THE Copley Medal of the Royal Society has been awarded to Professor J. Willard Gibbs, of Yale University.Director W. W. Campbell, of the Lick Observatory, has been elected an associate member of the Royal Astronomical Society.-Professor F. LamsonScribner, of the United States DepartIment of Agriculture, has been given charge of the Bureau of Agriculture established in the Philippines.

THE most important scientific news of the month is Mr. Carnegie's offer of $10,000,000 to endow a national university or institution for scientific research at Washington. The national government hesitates to accept the bonds of the United States Steel Corporation offered by Mr. Carnegie, but That there would be plenty of room this is a detail which will doubtless be for a thousand million suns in the arranged.-On the same day that Mr. assumed sphere is shown by a striking Carnegie's gift became known, it was calculation made by Kelvin. Thus, if announced that Mrs. Stanford had the suns were placed severally at the signed the final papers transferring centers of the thousand million cubes property, estimated at $30,000,000, to into which their enclosing sphere may Leland Stanford Junior University. It be supposed to be divided, then each appears that the endowment of Stansun would be nearly fifty million ferd is now about equal to the combined million kilometres from each of its six endowment of our three richest univernearest neighbors. This distance is a sities-Harvard, Col

PHOTOGRAPHED WITH THE TWO-FOOT REFLECTING TELESCOPE OF THE YERKES OBSERVATORY (RITCHEY).

STELLAR EVOLUTION IN THE LIGHT OF RECENT RESEARCH.*

BY PROFESSOR GEORGE E. HALE,

DIRECTOR OF THE YERKES OBSERVATORY,

UNIVERSITY OF CHICAGO,

ANY attempts have been made to sum up the work of

MANY attempts have

the nineteenth century, and to define its principal lines of progress. In estimates of the relative importance of the books published during this period there has been some divergence of view, but regarding one of them no element of doubt seems to have entered the minds of the critics. By unanimous consent Darwin's 'Origin of Species' is accorded a commanding position among the works which have influenced the intellectual life of the century. It would be difficult to overestimate the effect which the doctrine of evolution has wrought. The principle of orderly and harmonious development which it embodies has found application, not only in explaining the wide diversity of organic species, but in unifying the events of history, in elucidating the origin of language, and in throwing light on difficult questions in every department of human knowledge. The idea of evolution may indeed be traced back through the writings of many centuries. The early philosophers, though not possessed of the immense collection of recorded phenomena by which modern men of science may test their theories, were constantly occupied with great problems demanding the widest generalization. In attempting to account for the earth and its inhabitants they made the first steps in the direction which Darwin subsequently pursued.

Revised from an address delivered on June 5, 1901, before the Minnesota Chapter of the Honorary Scientific Society of Sigma XI, University of Minnesota.

It would be interesting to recall the strange traditions in which primitive peoples have recorded their vague imaginings of the origin of things. But the absence of even an attempt at careful reasoning renders such tales of no value for our present purpose. The Greek philosophers were not oblivious to the value of observation as a check on speculation regarding the solar system, but the instruments then available were too crude to give accurate positions of the heavenly bodies. Even Copernicus, though he established the sun at the center of our system, and thus paved the way for the nebular hypothesis, retained the epicycles of the Greeks. Kepler, basing his investigations. upon the observations of Tycho Brahe, proved that the planets move in ellipses with the sun at the focus, and removed all vestige of doubt as to the general plan of the solar system. The harmony which characterizes the motions of the planets and a knowledge of the effect of gravitation led Kant to formulate an explanation of the origin of the solar system, which subsequently found more perfect expression in the nebular hypothesis of Laplace.

In this hypothesis Laplace seeks to account for the formation of the sun and planets through the contraction of a vast nebulous cloud, which once filled the entire solar system, extending to the orbit of Neptune. This mass, which he considered to be fiery hot, was supposed to be in rotation. As it cooled, through radiation into space, it contracted toward the center. The result of this contraction was to increase the velocity of rotation, and when through increasing velocity the centrifugal force at the periphery counterbalanced the attraction of the central mass, a ring was thrown off. Further contraction resulted in the formation of other rings, in each of which the matter collected about its densest part, and thus produced a planet. Before they had time to cool these planets in turn threw off rings, which, with the single exception of Saturn's ring system, condensed into satellites.

This celebrated hypothesis, though unsupported by mathematical proof, has occupied a dominant position since the time of its publication more than a century ago. It has been subjected to much criticism, but most of the objections raised by Faye and others have been met by modifications of the hypothesis. Of late it has encountered fresh attacks on the part of Chamberlin and Moulton, and it now seems doubtful whether it will be possible to overcome their criticisms, which are based on dynamical considerations. It may prove to be sufficient, however, to forsake the lenticular mass of vapor predicated by Laplace in favor of the spiral form which Keeler has shown to characterize so many nebula.

The nebular hypothesis seeks to account for a system like our own, wherein a central sun is surrounded by planets and satellites, originally self-luminous, but ultimately cooled to the point where they are lumi