much less for violet and ultra-violet rays than for red and infra-red ones, we probably get infra-red rays from deeper-lying and hence hotter layers in the sun than we do ultra-violet ones.

We conclude that the solar radiation comes from sources ranging in temperature perhaps between the limits 5,000° and 7,000° absolute centigrade, but mostly from sources between 6,000° and 7,000°.

Washington observations.-Further experiments have been made, under Mr. Fowle's direction, on the transmission of radiation of great wave lengths through long columns of air containing known qualities of water vapor. Many of these observations are not yet reduced, so that it is not yet proper to give a numerical summary of results. The length of the column experimented upon has been increased to 800 feet. The measurements cover the infra-red spectrum, from the A line to a wave length of about 17μ. The observations of the water contents of the air column are made by means of pairs of wet and dry thermometers located at a number of points along the path. The air is thoroughly stirred before readings. Check experiments by Mr. Aldrich, in which he drew the air through phosphorus pentoxide tubes and weighed the water absorbed, have confirmed the accuracy of the water-vapor determinations. Mr. Fowle has made a preliminary comparison of the upper infra-red spectrum bands p, σ, 7, 9, Y, and , as observed through the tube with the same bands as observed through the whole atmosphere at Washington, Mount Wilson, and Mount Whitney. The results are most interesting, though not yet ripe for publication, and will probably lead to more exact knowledge of the total quantity of water vapor in the atmosphere, and its variation with the altitude of the observer and the season of the year.

FIG. 3.-Abbot silver disk pyrheliometer.

Reduction of observations.Upward of 100 days of solarconstant measurements have

been made on Mount Wilson on each of the last several years. Each day requires the equiva lent of three full days of computation. This work

is being done at Washington by Messrs. Fowle and Aldrich and Miss Graves and certain graphical parts of it by minor clerk Segal. The solar-constant reductions are computed as far as the middle of the observing season of 1910. Pyrheliometry.—Additional comparisons of the Mount Wilson secondary pyrheliometers have been made with primary standard pyrheliometer No. 3. These are not yet all reduced, but such as have been finished confirm the results of the previous fiscal year, so that we may regard the scale of absolute pyrheli

ometry as now satisfactorily established, and with it the mean value of the solar constant of radiation for the epoch 1905-1910 as fixed at 1.922 calories per square centimeter per minute.

Additional copies of the secondary silver-disk pyrheliometer shown in the accompanying illustration (fig. 3) have been standardized and sent abroad by the Institution as loans or purchases. There have now been sent copies to Russia, Germany, France, Italy, England, Peru, Argentina, and several within the United States, making in all 10 copies now in other hands than ours, besides several now being made to order. The Institution has undertaken the business relating to furnishing these pyrheliometers, which are standardized at the Astrophysical Observatory, to promote exact knowledge of the sun and its possible variability.

SUMMARY.

The year has been distinguished by a successful expedition to Mount Whitney. The results obtained there confirm the view that determinations of the intensity of the solar radiation outside the earth's atmosphere by the spectrobolometric method of high and low sun observation are not dependent on the observer's altitude above sea level, provided the conditions are otherwise good. The Mount Whitney expedition furnished opportunities also for measurements of the brightness of the sky by day and by night, the influence of water vapor on the sun's spectrum, and the distribution of the sun's energy spectrum outside the atmosphere.

Solar-constant observations and closely related researches were continued daily at Mount Wilson until November, 1910, and were taken up again in June, 1911.

Further research tends to confirm the conclusion that the sun's output of radiation varies from day to day in a manner irregular in period and quantity, but roughly running its courses within periods of 5 to 10 days in time and 3 to 10 per cent in amplitude. Assurance seems now complete that this result will be tested in the next fiscal year by long-continued daily observations made simultaneously at two widely separated stations.

Many copies of the silver-disk secondary pyrheliometer have been standardized and sent out to observers in this and foreign countries to promote exactly comparable observations of the sun's radiation.

Measurements of the transparency, for long-wave radiation, of columns of air containing known quantities of water vapor have been continued, and promise highly interesting results.

Respectfully submitted.

Dr. CHARLES D. WALCOTT,

C. G. ABBOT, Director.

Secretary of the Smithsonian Institution.

APPENDIX VI.

REPORT ON THE LIBRARY.

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, 1911, which was prepared by Mr. Paul Brockett, assistant librarian, who had charge until June 1, 1911.

The following improved methods and consolidation of work have been adopted during the past five years by the Library, in the interest of economy and efficiency:

The catalogue has been modified so as to include the author and donor cards and all previous records, thus making it necessary to consult only one file of cards for any information relating to the contents of the Library. The accession record is typewritten on sheets in accordance with the loose-leaf binding system, thus saving the time of copying titles by hand. The annuals have been transferred from the periodical record to the author catalogue, thus avoiding the making of two entries.

A new system of filing letters in numbered folders, with a card index, has been introduced, making easily accessible the correspondence which, in conjunction with the author and donor catalogue, forms a permanent record of the exchanges for the Smithsonian publications. The old files are gradually being rearranged and incorporated with the new system.

The lending of books in the reference room and periodical reading room has been placed in charge of one person, in connection with other duties.

The titles of purchased books are now entered on cards which are filed alphabetically. These card entries take the place of entries on sheets in book form, with card index.

With a thoroughly modern equipment in the way of furniture and fixtures greater improvements could be made than is possible at present.

Extension of space occupied by library.—Tentative plans have been prepared and submitted for fireproof bookstacks and bookcases for the large hall on the main floor of the Smithsonian Building to contain the libraries of the Government bureaus under the Smithsonian Institution. More definite plans are now in preparation.

International Congress of Archivists and Librarians and the International Congress of Bibliography and Documentation.-The Institution was represented by the assistant librarian, Mr. Paul Brockett, who presented a paper giving the views of the Smithsonian Institution in the matter of international exchange. At the same time he made observations on the methods and arrangement of European libraries. A separate report on this matter has been submitted by him.

ACCESSIONS.

For the Smithsonian deposit, Library of Congress, the accessions recorded numbered 3,136 volumes, 1,277 parts of volumes, 3,137 pamphlets, and 489 charts, making a total of 8,039 publications. The accession numbers run from 500,001 to 504,149.

The parts of serial publications entered on the card catalogue numbered 24,426, and 1,100 slips for completed volumes were made, and 100 cards for new periodicals and annuals.

These publications were forwarded to the Library of Congress immediately upon their receipt and entry. In their transmission 230 boxes were required, containing approximately the equivalent of 9,200 volumes. The actual number of pieces sent, including parts of periodicals, pamphlets, and volumes, was 26,286. This statement does not, however, include about 3,200 parts of serial publications secured in exchange to complete sets and transmitted separately. Inaugural dissertations and academic publications were received from universities at the following places:

Similar publications have been received from the technical high schools at Berlin, Braunschweig, Karlsruhe, and Munich.

The office library received 440 volumes and pamphlets, and 77 parts of volumes and charts, making a total of 517 publications. Thirteen volumes were purchased for the employees' library and one received by donation.

As already mentioned, an author catalogue, combining author and donor entries on cards of standard size was established this year and has taken the place of the previous "donor" record. Catalogue cards made for the authordonor catalogue numbered 3,199. In addition, a new finding list of 320 entries was made for the periodicals in the reading room, making a total of 3,519 cards. The recataloguing of scientific serials and annuals was commenced. The volumes recatalogued numbered 1,008.

The policy of sending foreign public documents presented to the Institution to the Library of Congress without stamping or entering has been continued, and the number of publications given above does not include these, nor does it include other publications for the Library of Congress received through the International Exchange Service.

The work of checking up and completing the Smithsonian deposit sets of publications of scientific societies and learned institutions of the world has been continued, and those of France have received special consideration.

DUPLICATES.

For a number of years about 10,000 duplicate Government documents returned by the Library of Congress, principally relating to statistics, were stored in the south tower of the Smithsonian Building. With the assistance of the International Exchanges during the previous year these publications were arranged and listed and later the larger part was turned over to the New York Public Library to complete its sets. Public documents of the United States were returned to the Superintendent of Documents.

EXCHANGES.

The establishing of new exchanges and the securing of missing parts to complete sets of publications in the Smithsonian Library required the writing of 2,600 letters, resulting in the addition of about 100 periodicals and in the receipt of about 3,200 missing parts.

The mail receipts numbered 32,647 packages, and 3,500 packages were received through the International Exchange Service. The publications contained therein were stamped and distributed for entry from the mail desk.

About 4,453 acknowledgments were made on the regular forms in addition to the letters which were written in acknowledgment of publications received in response to the requests of the Institution for exchange.

New exchanges of the annual reports of the American Historical Association from the allotment agreed upon for that purpose resulted in the acquisition of a number of publications of historical societies throughout the world, which were added to the Smithsonian deposit in the Library of Congress.

READING ROOM.

The periodical bins in the reading room were rearranged and, as already mentioned, a new finding list was made out on cards which were arranged alphabetically. Publications no longer consulted were transferred to the permanent sets, either in the Smithsonian deposit or in some one of the libraries of the Government branches of the Institution to which they belong. This gives the Institution and its branches a thoroughly useful periodical reading

room.

As many of the publications kept in this room are not to be found in other American libraries, they are consulted not only by Washington investigators, but by some from other centers. During the year the scientific staff of the Institution and its branches made use of 131 bound volumes of periodicals, and 2,949 parts of scientific periodicals and popular magazines. In addition, the various bureaus of the Government continue to avail themselves of the opportunity to use these publications, as well as those in the sectional libraries of the branches of the institution, and the library is frequently visited by investigators from all parts of the world.

ART ROOM.

No additions were made to the art objects or engravings in this room during the past year. With the additional space available for the use of the Division of Graphic Arts in the National Museum, it is expected that some of the engravings will be exhibited there.

THE EMPLOYEES' LIBRARY.

The books added to this library by purchase numbered 13, and one publication was presented. By binding, 415 volumes of periodicals were made available for circulation. The total number of books borrowed was 1,876. A number of books selected especially for the purpose were sent to the National Zoological Park, as in previous years.

LIBRARIES OF THE SMITHSONIAN BRANCHES.

United States National Museum.-The congestion in the museum library reported last year has been relieved to a certain extent by the temporary employment of four cataloguers and the assignment of space on two of the