of the sun be, which is absorbed at once on the walls of the chamber instead of indirectly by air convection.

The instrument is mounted equatorially and driven by clockwork, and the rate of flow of the water current, lapse of time and temperature change caused by radiation, are all recorded photographically on a moving drum. Hence a continuous automatic record of the solar radiation is produced. In use at Mount Wilson it is not easy to avoid considerable temperature change of the apparatus, and this causes a slight "drift" of the record, but not enough to prevent runs of several hours' duration without attention.

A considerable part of the apparatus for the continuous pyrheliometer was made by the International Instrument Company, of Cambridge, Mass. The more refined parts for the receipt and measurement of the radiation were constructed by Mr. Kramer at the Observatory shop. In this, and in a great amount of other work during the year, Mr. Kramer has combined skill with rare willingness and interest in a way which deserves commendation.

(3) THE EXPEDITION TO MOUNT WILSON, IN CALIFORNIA.

From the very beginning, in 1902, of experiments in Washington on the measurement of the solar constant of radiation it has been your aim to continue these measurements at a more favorable situation as regards cloudiness, and particularly as regards elevation. You long ago showed that in optical quality the lower air is far inferior to that lying above, and you have repeatedly stated your conviction that exact determinations of the absorption of the atmosphere are impossible at stations near sea level. Congress having approved of your plan to conduct these observations at high altitudes, apparatus has been collected during the past three years for an expedition to a favorable station for the measurement of the solar constant.

In the meantime the Carnegie Institution had been founded, and by invitation of one of its officers you stated, in a communication to the Hon. C'. D. Walcott, dated February 28, 1902, your belief that the establishment by the Carnegie Institution of an observatory to be situated at some high and cloudless point and engaged for at least a complete sun-spot cycle in the accurate determination of the solar constant of radiation would be a worthy astronomical undertaking and one most likely, in your judgment, to yield results of value both from the standpoint of pure science and from that of practical utility to mankind.

In 1904 the Carnegie Institution began the establishment of a solar observatory on Mount Wilson, in California, under the direction of Prof. G. E. Hale, and the objects of this observatory include the measurement of solar radiation, which you had urged. Almost immediately after the installation at Mount Wilson had been begun, Professor Hale, recognizing the large share you have had from the first in promoting the establishment of such an observatory, and knowing of the preparations making at the Smithsonian Astrophysical Observatory for an expedition to a high station to observe the solar constant, invited you to send this expedition to Mount Wilson, and promised all possible cooperation during its stay, and suggested that the work would, if desirable, be taken up by the new solar observatory when the Smithsonian expedition should be withdrawn. This invitation was accepted. The equipment, consisting of a full spectro-bolographic and pyrheliometric outfit, the equal and in some respects the superior of that installed in Washington, was sent forward in April, 1905. The observers, C. G. Abbot in charge, and L. R. Ingersoll, temporary assistant, reached the ground about May 10. Two shelters for the spectro-bolometer and the continuous pyrheliometer, respectively, already framed in the valley below.

were immediately erected on Mount Wilson, and were finished, including all their piers and accessories, in about two weeks. The spectro-bolometer was completely installed and the first bolographic observations were made June 6, 1905.

In the meantime observations had been made nearly every day with the mercury pyrheliometer, and these had given promise of great transparency and uniformity of sky. From the 1st of June hardly a cloud was ever seen above the level of the horizon for many weeks. Extraordinary calmness adds to the advantages of this site. A few of the earliest bolographs were measured at cnce to see if all appeared to be well, and, as the measurements turned out very satisfactorily, bolographic work was continued nearly every day thereafter, leaving the reduction of the observations to a later time.

Investigations at Washington, as already reported, have given strong grounds for the conclusion that the solar radiation varies considerably and frequently in its amount. It would be most desirable if the Mount Wilson expedition could give ample opportunity to test this conclusion, but in spite of the too short time at present command it has been thought best by you to initiate it, and at the same time to study more closely the manner of the solar variability. To this end the work includes, not only solar-constant measurements, but other studies designed to add to our knowledge of the whole question.

The expedition is under the greatest obligations for the continued aid furnished by the director and staff of the Carnegie Solar Observatory. The results obtained will doubtless form a principal part of next year's report.

SUMMARY.

The principal object of the Observatory during the past year has continued to be the measurement of the solar radiation. The work of this and the two preceding years strongly supports the view that the radiation of the sun is frequently diminished and augmented for periods of a few weeks or months, in consequence of a variability of the transparency of the solar absorbing envelope, and that this variation of radiation causes and quickly produces changes of several degrees in the mean temperature of the land areas of the earth. It is hoped that the study of the solar radiation will soon prove a valuable aid in forecasting climate.

Important additions and improvements have been made in the equipment of the Observatory, both in buildings and apparatus. The new apparatus includes a standard pyrheliometer, capable of continuously registering the solar radiation and provided with means of certifying the exactness of its measures independently of the theory of the instrument.

An expedition to measure and test the variability of solar radiation has been sent to Mount Wilson, in Southern California. Respectfuly submitted.

Mr. S. P. LANGLEY,

C. G. ABBOT,
Aid Acting in Charge.

Secretary Smithsonian Institution, Washington, D. C.

APPENDIX VI.

REPORT OF THE LIBRARIAN.

SIR: I have the honor to present the following report on the operations of the library of the Smithsonian Institution for the fiscal year ending June 30, 1905: The publications received by the Institution and recorded in the accession books of the Smithsonian deposit, Library of Congress, number as follows:

The accession numbers run from 460377-468086.

As in the past a few of these publications were retained at the Institution for the use of the scientific stuff, but the larger number have been sent direct to the Library of Congress. The entire sendings from the Institution required the use of about 274 boxes, which it is estimated contained the equivalent of 10,960 octavo volumes. This estimate does not include, however, a large number of public documents presented to the Smithsonian Institution and sent direct to the Library of Congress without recording.

At the close of the year ending June 30, 1904, there remained in the Museum library a number of the scientific series, together with books and pamphlets on special subjects, belonging to the Smithsonian deposit, to be withdrawn, checked, and sent to the Library of Congress, these publications having been held at the Museum when that Library was overcrowded in its old quarters at the Capitol. While 7,805 parts were transmitted during the past year, it has not been possible to complete the checking, owing to the fact that the time of the small force in the Smithsonian library was fully occupied with current work, but every effort will be made to finish the task before the close of the present year, when all of the series of periodicals and publications belonging to the deposit, with the exception of those in actual use, will be in the hands of the Librarian of Congress.

The libraries of the Secretary, Office, and Astrophysical Observatory have received during the year 418 volumes, pamphlets and charts, and 2,040 parts of volumes, making a total of 2,458, and a grand total, including books for the Smithsonian deposit and the Watts de Peyster collection Napoleon Bonaparte, of 35,820.

The parts of serial publications that were entered on the card catalogue numbered 26,000. One thousand seven hundred and thirty-five slips for completed volumes were made, and about 720 cards for new periodicals and annuals were added to the permanent record from the periodical recording desk,

Inaugural dissertations and academic publications were received from universities at the following places:

In continuing the Secretary's plan to effect new exchanges and to secure missing parts to complete sets, 1,405 letters were written, 301 new periodicals were added to the receipts, and 527 defective series were partly or entirely completed. In addition to the letters above referred to there were 175 postal cards sent asking for current numbers that failed to reach the Institution, which resulted in 103 being received.

The scientific staff and others have continued to consult the proceedings and transactions of the learned societies in the reference room, and from the reading room 21 bound volumes of periodicals were withdrawn and 4,368 scientific periodicals and magazines were borrowed for consultation.

The sectional libraries maintained in the Institution, the Secretary's library, Office library, and the Employees's library, together with those of the Astrophysical Observatory, Aerodromics, International Exchanges, and Law Reference, have been used by persons from the other scientific bureaus of the Government, as well as members of the immediate staff.

In the Secretary's and Office library 107 books were bound, and special attention was given to collating the publications in the Astrophysical Observatory, with the result that 118 completed volumes were bound at the Government bindery. At the National Zoological Park 8 volumes have been added to the library by purchase.

THE EMPLOYEE'S LIBRARY.

The popularity of the Employee's library has continued, and during the year 3,262 books were borrowed. The new books added to the library by purchase numbered 19, and 78 completed volumes of magazines were bound. The sending of about 40 of the books from this library to the National Zoological Park and 26 to the Bureau of American Ethnology each month has been continued with marked appreciation from the two bureaus.

THE WATKINS LIBRARY.

Within the last few months the trustees of the estate of the late Dr. J. Elfreth Watkins have turned over to the Smithsonian Institution his large and valuable library consisting in the main of books relating to engineering and transportation. A book plate has been provided and the books listed, and it is hoped that they may soon be available for the use of those interested in the subject to which they relate.

THE JOHN DONNELL SMITH LIBRARY.

Through the munificence of Capt. John Donnell Smith, of Baltimore, the library of the Smithsonian Institution has become enriched by his collection of botanical works, numbering about 1,600 volumes, containing books bearing upon the flora of tropical America, carefully selected and substantially and

artistically bound. This donation was, made in connection with the gift to the Institution of his herbarium, and brings to the National Museum, where the library will be deposited, an unrivaled basis of equipment for the prosecution of a complete botanical exploration of Central America and a critical study of its whole flora.

WATTS DE PEYSTER COLLECTION NAPOLEON BUONAPARTE,

It is very gratifying to report the rapid increase of the Watts de Peyster Collection Napoleon Buonaparte through the continued gifts of Gen. John Watts de Peyster. The additions during the year numbered 1,775 volumes and 1,007 maps.

INTERNATIONAL CATALOGUE OF SCIENTIFIC LITERATURE.

The Institution has continued to act as the representative in the United States for the International Catalogue of Scientific Literature, and has indexed and classified for the Central Bureau at London the scientific literature of the United States. During the past year the number of references sent to the Central Bureau at London was 24,182, an increase of nearly three thousand over the previous year, as follows:

All of the first annual issue of the International Catalogue has been published, together with all of the second annual issue, excepting the volume of Zoology and five volumes of the third annual issue, namely, Mathematics, Mechanics, Physics, Astronomy, and Bacteriology.

MUSEUM LIBRARY.

In the Museum library there are now 24,170 bound volumes and 38,643 unbound papers. The additions during the year consisted of 3,573 books, 3,048 pamphlets, and 563 parts of volumes. There were catalogued 1,952 books, of which 101 belonged to the Smithsonian deposit, and 3,755 pamphlets, of which 185 belonged to the Smithsonian deposit, and 12,216 parts of periodicals, of which 1,309 belonged to the Smithsonian deposit. In the accession book 3,573 volumes, 3,048 pamphlets, and 563 parts of volumes were recorded. The number of cards added to the author's catalogue was 5.942, which does not include 847 cards for books and pamphlets recatalogued.

In connection with the entering of periodicals 55 memoranda were made reporting volumes and parts missing in the sets, together with a few titles of publications that were not represented in the library. The result of this work was the completing or partly filling up of 23 sets of periodicals.

Throughout the whole year attention has been given to the preparation of volumes for binding, with the result that 1,371 books were bound, and at the close of the year there were several hundred more ready for the binder.

The number of books, pamphlets, and periodicals borrowed from the general library amounted to 40,400, including 9,192 which were assigned to the seetional libraries.