the same way. The other group, typified by U Geminorum and SS Cygni, are normally very faint, but at irregular intervals (of two or three months for the last named star) increase rapidly by some four magnitudes, to fade away again after a few days. It is a curiously suggestive fact that the stars of each of these singular classes are very similar to one another in spectrum, while the spectra of each class as a whole are quite unlike one another or anything else in the heavens. Here is indeed a riddle for the future to solve. Finally, we come to the temporary stars-those most spectacular of all celestial objects. To discuss them fully would require another address comparable in length to this. The merest outline must suffice. Before the outburst, several of them are known to have existed as faint stars, often slightly variable. Without warning and within a very few days at most, their light increases at least a thousand fold— sometimes fully a hundred thousand times. The happy chance by which the recent great Nova in Aquila was caught midway in the rise indicates that its whole ascent occupied about two days. The maximum brightness is sometimes very great.-Tycho's star of 1572 equalled Venus-but a rapid decline sets in almost at once, followed by irregular oscillations with a general downward tendency, merging into a slower but steady decline, till within a decade or so the star has lost eight or ten magnitudes and returned nearly to its original brightness. The spectroscopic changes are meanwhile of the most extraordinary character. The three stars which have been caught on the rise showed dark line spectra, roughly resembling familiar types, but no two alike, and with the lines greatly displaced, as if by a huge velocity of approach. As the star goes 66 over the top" its spectrum explodes, so to speak, in a few hours into a flamboyant affair of bright and dark lines, enormously widened and displaced, and undergoing continual changes. Lines of hydrogen, helium, and enhanced metallic lines. have been recognized. Besides the bright hydrogen lines in Nova Aquile there were at times two sets of sharp dark lines-apparently due to hydrogen, but displaced by amounts corresponding to velocities of approach of about 1,800 and 2,600 km./sec. Complicated changes occur as the light fades, the most important being the appearance of the characteristic nebular lines, which at some stages are the most conspicuous feature of the spectrum, and remain visible for a long time. After some years, however, they begin to fade, and the last state so far recognized is spectroscopically identical with the Wolf-Rayet stars. Nove show a very strong galactic condensation. Nothing is known of their proper motions, or (for obvious reasons) of their peculiar velocities; but direct measures of parallax indicate that the distances of some of the brighter ones are of the order of at least 100 parsecs. They must therefore be exceedingly bright objects at maximum; but how bright we do not know. These objects bear very remarkable relations to nebulæ. They appear to be related spectroscopically to the gaseous nebulæ. The unique moving nebula near Nova Persei was admirably explained by Kapteyn as due to the illumination of a sheet of diffuse matter, nearly at rest, by the outgoing light of the great outburst-a hypothesis confirmed by Slipher's recent discovery that two variable nebulæ appear to shine by reflected light from their nuclei, which show spectra very similar to novæ. Most remarkable of all is the recent discovery that novæ appear in the spiral nebulæ so fast that it would take intensive observations to catch them all. It is obvious that in these temporary stars we are in the presence of catastrophes, which in magnitude utterly transcend all other known physical phenomena. And these catastrophes are not of rare occurrence, but happen every few years, or oftener, in the galaxy, and apparently every few weeks in the Andromeda nebula. Two possibilities suggest themselves at once a collision or an internal explosion. Collisions between two stars are quite out of the question-owing to the frequency and short duration of the phenomena. The hypothesis of a collision between a star and a nebula meets these two fundamental objections, and appears capable of accounting qualitatively for many or most of the phenomena, as was shown some years ago by Seeliger. But the spectroscopic data, and especially the darkline spectrum on the rise, remain difficult to explain. A collision between a star and a relatively small dark body-recently postulated by W. H. Pickering-is also worthy of consideration, but presents difficulties of its own. After what we now know and believe regarding the stores of energy which are locked up in the nuclei of atoms, the hypothesis of an explosive release of some such form of energy within a star can not be neglected. The chief difficulty about it seems to be that we might expect an even greater catastrophe than appears to occur but this theory will probably prove to be increasingly flexible as our knowledge advances. At present, however, the collision theory appears to the speaker the most promising. The great frequency of novæ in the spiral nebule-where we might expect collision to occur, if anywhere in the universeseems to be favorable to this view. In concluding this hasty and imperfect survey of a wide field, two things stand out prominently-first, the importance of a study, which was once neglected and even rather despised, in the attack upon some of the most fundamental problems of astrophysics, and, second, the urgent need of extensive and active researches, observational, statistical and theoretical, to advance toward solutions of some of the many unsolved problems which still remain before us. HENRY NORRIS RUSSELL PRINCETON UNIVERSITY OBSERVATORY, CHARLES ROCHESTER EASTMAN1 On this side of the Atlantic there have been few zoologists who have devoted their lives to the study of ancient fishes-which for the rest concerns not a few of the greatest problems of the vertebrates. Of investigators 1 Born Cedar Rapids, Iowa, June 5, 1868, died Long Beach, N. Y., September 27, 1918. who have passed away we recall the distinguished names of Agassiz the elder, Cope, Newberry and Leidy, and to this goodly fellowship we must now add the name of Charles Rochester Eastman, whose services have contributed widely and intensively to a knowledge of fossil fishes. To this work he gave his time devotedly for a quarter of a century, publishing over a hundred papers, among them a number of monographs which rank among the most scholarly and accurate in their field. Eastman graduated from Harvard in 1891, studied at Johns Hopkins, thereafter in the University of Munich, where he took his doctorate in 1894; he worked with Professor Karl von Zittel, whose laboratory then attracted a number of young American paleontologists. Here, as Eastman's interests already centered in fossil fishes, he was given the only material for research which the German university had at hand-a mass of detached teeth of a Chalk Measures shark-not attractive material, to say the least, but the young investigator attacked it with energy and soon gathered the data for a successful thesis. He was next given a post at Harvard, where in the Museum of Comparative Zoology, under the mantle of Louis Agassiz, he reviewed the collections of early fishes and found much material for publication. He now became interested in the Devonian fossils of the Agassiz collection, which he found shed light upon the rich finds from the Middle West, then being described by Dr. Newberry. Eastman's imagination was especially touched by the range and character of placoderms" as the dominant group of Devonian times, and like many another worker, he set himself to solve the puzzles of their lines of evolution and of their kinship to modern fishes. Hence he sought actively for more extensive and better preserved material upon which to base his findings. The best collecting ground for these American forms was in Ohio, and throughout this region Eastman soon learned to know the fossil hunters and their collections. His studies upon these forms thereupon spread over wider fields, and became well-nigh encyclopædic; he brought the entire Devonian 66 fish fauna under his finger tips, literally: and if Eastman were sought for at this time, he would have been found at the top of the Agassiz Museum in the center of a labyrinth made up of tiers of great trays of fossils: and the visitor would come away with the impression that there was something almost uncanny in the skill with which Eastman could call up out of the mud-colored shales these primæval creatures, for their membra disjuncta would be made to fit in place so quickly, so faultlessly, and sometimes with so audible a click that one could almost picture the fish coming to life in its tray. From the study of placoderms, Eastman's studies extended naturally to the contemporary lung-fishes and ganoids, and to our knowledge of these early forms he made numerous contributions. Now and again he would hark back to the group of sharks, trying ever to bring order into this primitive and difficult group. Port Jackson sharks, with their curiously modified dentition, which enabled them to crush the shells of shellfish, suggested new lines of evolutional changes, and his work on these forms from Illinois, Iowa, Missouri, Kansas and Nebraska showed new sequences and enabled him to fill out the gaps in their history. Certain of these early sharks became so similar to lung-fishes in their dentition, that, on this evidence alone, the two great groups of fishes might readily have been merged. During the last decade of his work, Eastman's attention was drawn more closely to types of modern fishes. This was perhaps due to the fact that he had been able to bring to this country the famous collection of a Belgian paleontologist, de Bayet, and install it in the Carnegie Museum at Pittsburgh. Upon the fishes of this collection, especially those from northern Italy (Monte Bolca) he published a number of beautiful memoirs. In matters relating to the phylogeny of fishes, Eastman was conservative. Thus, following Smith Woodward, he maintained that the group of placoderms which the latter defined as Arthrodira was definitely related to primitive lung-fishes: he had little sympathy with those who believed that they had solved the riddle of Tremataspis and Bothriolepis by associating with them arthropods. As a systematist, Eastman was thorough, and the forms which he described will rarely need revision.2 2 Mrs. H. J. Volker has recently reviewed the papers of Dr. Eastman, and summarizes his systematic contributions as follows: New families: (3) Histionotophorus. New species: (115) Acanthodes beecheri; marshi. Asthenocormus retrodorsalis. Carcharias collata; incidens. Chanoides leptostea. Cladodus aculeata; prototypus; urbs-ludovici. Coelacanthus exiguus; welleri. Calogaster analis. Conchodus variabilis. Ctenacanthus acutus; decussatus; longinodosus; Dinichthys dolichocephalus; livonicus; pelmensis; Dipterus calvini; costatus; digitatus; mordax; pectinatus; uddeni. Elonichthys disjunctus; perpennatus. No one can recall Dr. Eastman without bringing to mind his keen appreciation of ancient literature. He read the classical texts fluently, and Aristotle and Pliny had to him the interest of modern authors. Perhaps he knew them and their kindred better than did any living paleontologist. For bibliographical work Eastman had ever a distinct leaning, for to know what others had done in a definite field was the only honest beginning of any research. It was this interest which led him to accept the invitation of the American Museum of Natural History to undertake the editorship of a bibliography of fishes which the museum was engaged in publishing, and it was under his supervision that the two first volumes of this work appeared-ever to lighten the labors of workers in this field. SCIENTIFIC EVENTS THE FOREST SERVICE IN WAR TIMES How the Forest Service met its war responsibilities is the main subject discussed by its chief, Henry S. Graves, in his annual report to Secretary Houston, just published. The war led, he asserts, to the temporary abandonment of many of the old lines of work, the curtailment of others, and the assumption of large new duties. Because of the close relation of the National Forests to the economic life of the country and to the production of necessities never before so urgently required, "their continued administration along lines which would prevent the breakdown of any essential industry was an obvious duty." At the same time the Forest Service was employing its technical knowledge and equipment for the furtherance of war preparations involving the use of forest products, in response to the many demands of the War and Navy Departments and the war industries. There were furnished to the Army and Navy 446 men, while a considerable number left to serve in the War and Navy Departments in a civil capacity and to take part in industries directly concerned in producing materials for war uses. Still others were forced to leave the service because with the low standard of salaries, they were unable to meet the rising cost of living. All told, 1,179 persons had gone from the service prior to October 1. The situation of the Forest officers, clerks and others having fixed bases of salary is regarded by the forester as very critical, requiring the earnest consideration of Congress. The receipts from the National Forests were slightly greater than in 1917, with a total of not quite $3,600,000. The grazing business produced an increase based on the land classification work, the area showed a slight net reduction, leaving the amount of governmentowned land in the forests at the close of the year 155,927,568 acres. Regarding the land classification the report says: After nine years of steady sifting to separate from the forests such lands as should not be retained permanently in public ownership, the task has, except in Alaska, been brought substantially to completion. The existing forests are approaching stability. Hand in hand with the cutting down of the forests, a movement in the opposite direction has taken place, which has the same basic purposes to provide for the highest use of the land; and this movement, the report states, is growing stronger. This is due primarily to the demonstration of the public advantages realized through government ownership and administration. A memorial of the state of Idaho is cited, asking Congress to include in the National Forests an area of over one million acres in that state which is now contributing little or nothing to the wealth of the state but is undergoing deterioration. This addition, says the report, should unquestionably be made. The report deals fully with the numerous and important investigations made for the benefit of war activities. Practically the entire research organization was placed on special war investigations and was increased in size more than five times to meet the demand for information. Among the most urgent problems were those connected with the construction of aircraft, and a vast amount of information applicable in airplane construction was obtained. Practically all the war work branches of the government having to do with the purchase of wood materials were added, including in the Army the General Staff, the Bureau of Aircraft Production, the Ordnance Department, the Signal Corps, the Quartermaster Department, the Engineer Corps the Gas Warfare Department and the Surgeon General's Office; in the Navy the Bureaus of Construction and Repair, Steam Engineering, Yards and Docks, and the Navy Yards; the Shipping Board; the Emergency Fleet Corporation; the Director General of Railroads; the War Industries Board; the War Trade Board, housing organizations; the Fuel Administration, and the Food Administration. In addition, cooperation and assistance was given the Allied Governments and to the industries furnishing war materials. |