The Wagon Wheel Gap Experiment Station has also been continued. This station is maintained in cooperation with the Forest Service of the department as in former years. Since the first phase of the experiment is drawing to a close, arrangements have been made looking to a discussion of the meteorological data that have been accumulated in the last seven years.

PRINTING AND PUBLICATIONS.

The utmost economy was practiced throughout the year in the issue of publications and in the purchase of the necessary supplies of paper, ink, and other printing materials. Nevertheless, the usual series of periodical and nonperiodical publications have been adjusted to war conditions and issued much as usual, including some new publications which have more or less definite relations to war work.

A careful revision of mailing lists justified dropping the names of a number of recipients of periodical publications whose interest in the same ceased to be active for one reason or another.

Large and frequent demands were made for such Weather Bureau pamphlets, reprints, etc., as are of value in military instruction and practice, especially in aviation, and these were promptly and liberally filled to the extent of our resources. The requests were made not only officially by bureau chiefs, commanding officers, and instructors, but also in large numbers by individual officers and enlisted men stationed at the various camps throughout the country.

Since the beginning of the war the distribution of publications to foreign addresses by mail and international exchange has gradually been reduced to a comparatively small number of copies. At present the service is discontinued to all the central powers and their allies, and to countries wholly or in part occupied by them. A limited reserve of the more important publications is maintained in our stock for supplying authorized foreign demands after the cessation of the war.

All the material for the Monthly Weather Review was prepared and submitted on schedule time, and the data for the Annual Report of the Chief of Bureau, 1916-17, were collected, compiled, and the volume issued at the time prescribed by law. Considerable data regarding the occurrence of tornadoes and hail storms were collected, and the text, indicating some of the details of these storms, together with appropriate charts showing their distribution throughout the country, form valuable additions to the report.

The monthly and annual summaries of the State climatological services were prepared along the usual lines, and with a few exceptions were issued on schedule time. The printing of a climatic summary for Alaska, similar to those for the States, began with January, 1917, and most of the issues for that year have been printed. It is probable this work will soon be brought up to date.

No material changes were made in the snow and ice bulletins issued last winter at the central office, or for the mountain States of the West, except that a few additional reports have been provided for in some of the higher mountains where observers have not heretofore been available.

A short report on the climate of France and Belgium was prepared during the year, and by publication in the Weather Review and the monthly summaries of the State climatological services received an unusually wide distribution.

The preparation of data for the atlas of American agriculture was carried forward to near completion. The text sections on temperature and miscellaneous data were completed, as well as the major part of the necessary drafting work, and some of the folios have been printed and will soon be available for distribution.

In response to the needs of aviators and other students of the atmosphere, an effort has been made to bring together as much as practicable of the important knowledge of the physics of the air. The publication of this without cost to the Government was begun as a serial in the Journal of the Franklin Institute, August, 1917, and continued through the year.

In cooperation with the Smithsonian Institution, the Smithsonian meteorological tables have been extensively revised by officials of the Weather Bureau and republished by the Smithsonian Institution.

Considerable progress has been made on a paper discussing the more important weather features attending the severe cold of last winter. It was expected that this would be completed before the end of the fiscal year, but it has been delayed by press of routine work and failure so far to receive reports from some far northern districts.

LIBRARY.

During the year, 827 books and pamphlets were added to the library, the same number as last year. The total strength of the collection is now about 37,100. The library has been utilized extensively by men undergoing training for the meteorological work of the Army and the Navy and has lent a considerable number of books for use at the front. A brief bibliography was prepared on the subject of military meteorology.

The number of promotion examination papers rated during the year was 32, of which 28, or 87 per cent, received passing grades. The promotion examinations, which, with some variations in form and scope, have been in operation since 1899, were discontinued May 4, 1918. This course does not imply any lowering of the standards of qualifications for entrance or eligibility for advancement, but rather the reverse, because a new entrance grade has been established, examinations for which are held as frequently as necessary by the Civil Service Commission.

SEISMOLOGICAL INVESTIGATIONS.

The systematic work of collecting and publishing earthquake data, begun December 1, 1914, was continued during the year. These data are of two kinds-noninstrumental reports of earthquakes felt and instrumental records, often of quakes wholly imperceptible to the senses. The noninstrumental reports are rendered by all the regular stations of the bureau, nearly 200 in number, and also by nearly all the bureau's 4,500 cooperative observers. The instrumental records published by the bureau have been obtained in part by instruments

owned and operated by the bureau itself, one at Washington, D. C., the other at Northfield, Vt. The remainder are furnished through cooperation with various agencies at 18 additional stations distributed from Panama to Alaska and from the Hawaiian Islands to Porto Rico.

During the calendar year 1917, 112 earthquakes were felt within the borders of the United States proper. The great majority of these produced no damage whatever, and none any material damage.

SOLAR RADIATION INVESTIGATIONS.

Continuous records of the total amount of radiation received on a horizontal surface from the sun and sky were obtained throughout the year at Washington, D. C., Madison, Wis., and Lincoln, Nebr. Measurements of the intensity of direct solar radiation have been made at the above stations, and also at Santa Fe, N. Mex., whenever atmospheric conditions have been suitable, and at Washington and Madison the percentage of polarization of sky light has been measured. A monthly summary of the results has been published in the Monthly Weather Review.

Experience has shown the superiority of the silver-block type of Marvin pyrheliometer over the spiral-ribbon type. Two new instruments of the former type have therefore been constructed and standardized during the year to replace instruments of the spiral-ribbon type in use at Lincoln and Madison. A similar change in the instrumental equipment has also been made at Santa Fe, so that all four pyrheliometric stations are now equipped with the new and improved form of Marvin pyrheliometer.

Persistent requests have been received from various sources for the cooperation of the Weather Bureau in a project having for its object the determination of sky brightness, or the intensity of natural lighting, in various sections of the United States, at different seasons of the year and hours of the day, and under various atmospheric conditions. Some preliminary work has been done along this line.

A program for meteorological observations was planned for about 55 Weather Bureau stations in or near the path of total obscuration of the sun during the eclipse of June 8, 1918. In addition, a special station for measuring both incoming and outgoing radiation during the eclipse was established at Goldendale, Wash., at the center of the path of totality. The complete program was carried out as planned, although weather conditions at some points were unfavorable.

The Office of Solar Radiation Investigations at Camp American University has cooperated with the experiment station of the Bureau of Mines (now the Chemical Warfare Service, National Army) in determining the prevailing meteorological conditions during experiments in the open air.

AGRICULTURAL METEOROLOGY.

With the growth and extension of the service rendered by the Weather Bureau and represented by its great weather and crop service, the establishment of the Division of Agricultural Meteorology to handle all such work under capable direction was the natural outcome. This organization became effective February 21, 1916, and has

been described in previous reports. Its activities have been continued, improved, extended, and given specially direct application as far as possible to all agricultural activities of the Nation now so directly concerned in food production and conservation.

In addition to its function of supervising and directing the weather and crop service, this division is also responsible for conducting studies of many different kinds. Without attempting to describe the various special investigations comprised within the operations of this division, the following brief outline will indicate the extent and character of its activities:

CORN AND WHEAT REGION SERVICE.-Covers 16 principal grain States, with the region center at Chicago, Ill., and 188 special reporting stations.

COTTON REGION SERVICE.-Covers 11 principal cotton States, with the region center at New Orleans, La., and 165 special reporting

stations.

SUGAR AND RICE REGION SERVICE.-Covers the rice and sugar cane growing sections of the South, with 6 special-reporting stations.

CATTLE-REGION SERVICE.-Covers all or parts of eight grazing States, with 67 special-reporting stations. This service was changed in the spring of 1918 from a daily service during the summer months to a weekly service throughout the year. This change is proving to be of decided advantage.

SPECIAL FORECAST AND WARNING SERVICES. Special stations are maintained in the principal tobacco, potato, alfalfa seed, cranberry, citrus, and deciduous fruit-growing regions, to aid in special forecasts and minimum temperature warnings, and have proved to be of marked value in this connection.

COOPERATION.-The Weather Bureau is cooperating with other bureaus and departments in maintaining special stations for the benefit of science and agriculture. Such stations are maintained in 14 different States.

PROTECTION OF ORCHARD AND TRUCK CROPS FROM FROST.-Considerable time has been devoted to the making of temperature and air-drainage surveys in citrus and deciduous orchards in the West, and in studying orchard-heating problems. Officials of the bureau have been placed in the principal districts where orchard heating is extensively practiced to aid in making and distributing minimum temperature forecasts.

FROST STUDIES IN NORTH CAROLINA. For several years the bureau has been conducting frost and temperature studies in North Carolina. During the year the final report of the discussion of nearly five years' accummulated data was submitted and is undergoing careful examination and consideration with the view to ultimate publication.

THE EFFECT OF THE WEATHER UPON CROPS. -The Division of Agricultural Meteorology has continued its study of the relation between weather and climate, and crops. Data have been collected and tabulated and results obtained which are proving of marked advantage to agriculture.

THE NATIONAL WEATHER AND CROP BULLETIN.-The preparation and issue of this bulletin continue to take the greater part of the time of the force of this division during the crop season. It is published weekly from April to September, inclusive, and monthly during the winter season. A new feature during the past season has been the inclusion of data regarding the planting and harvesting of the principal crops, at the request of the Office of Farm Management, as an aid in determining the labor requirements. The results of the correlation of weather and crops have been published in this bulletin from time to time.

PACIFIC COAST WEATHER AND CROP SERVICE.-A special weather and crop service covering the States of Arizona, Utah, Nevada, Idaho, Washington, Oregon, and California, was inaugurated at the beginning of the 1918 crop-growing season, with San Francisco as the district center. A bulletin somewhat similar to the National Weather and Crop Bulletin was issued at the district center each Wednesday from April to September, inclusive, and will be continued monthly during the winter season.

INSTRUMENTATION, TESTS, AND REPAIRS.

The closing of European markets for scientific apparatus, accompanied by the great congestion of manufacturing work in this country, has presented serious difficulties to the Weather Bureau in procuring the necessary high-grade instruments for its work and has imposed upon what was formerly known as the instrument division of the bureau many additional duties, since it became necessary in certain respects at least to undertake to construct here instruments which could not possibly be procured elsewhere. In fact, we have with limited facilities endeavored to extend aid to the Army and Navy in constructing meteorological instruments to meet special needs. Under these conditions it became necessary to reorganize this part of the work of the bureau and to divide the original instrument division into two parts, one devoted to general administrative affairs connected with the receipt and issue of instruments and their exposure at stations, the other to be concerned with the testing of new instruments, the construction and repair of instruments, and their careful adjustment to meet station requirements. Even at best the difficulty of maintaining necessary supplies to meet all needs has been serious, and more or less delay has necessarily marked the progress of this part of our work. As time goes on and as American manufacturing interests become more able to meet requirements which in many cases formerly were supplied from European sources, a general improvement must result.