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INFRA-RED SOLAR SPECTRUM OF A 60° ROCK-SALT PRISM, b.

A determination has been made of the change in deviation of the A line with change of temperature of the salt prism. The value obtained was -12.0"0.4" for the change in deviation, corresponding to 1° rise in the temperature of the prism. Interesting results were obtained, experimentally, showing that for slit widths less than 0.15 millimeter the increase in the loss of energy by diffraction is very rapid. An investigation was begun, and bids fair to end successfully, with the design of constructing a galvanometer far more sensitive than the one in present use, which may enable a considerable gain to be made in the number of lines to be discovered by the bolographic method of spectrum analysis.

ACQUISITIONS AND ALTERATIONS OF APPARATUS.

1. A concave mirror 26 centimeters in diameter and of 230 centimeters principal focal length was obtained for use in the system of collimation by two mirrors, as proposed in last year's report, and actually installed with advantage in August, 1896. The metal work required in the mirror mountings was done at the Observatory shop. 2. Three very accurate optical flats, 12 centimeters in diameter, were procured for testing the faces of the salt prism during its occasional polishings, and for use as plane mirrors when required.

3. A train of totally reflecting prisms, so adjusted as to invert an image, was obtained for use with the 6-inch telescope as an erecting eyepiece.

4. A number of large blocks of sait were received through the courtesy of the Russian Government, and from one of the blocks, which promised good optical quality, there was cut a large prism. On polishing, however, the quality of the interior was found to be so far below the exterior appearance that the prism has not been made use of. The optical work on the pieces of apparatus above mentioned was done by Mr. J. A. Brashear.

5. A Zeiss anastigmatic wide-angle photographic lens was procured for use in photographing interior rooms.

6. A Nachet compound microscope with mechanical stage and various accessories was obtained and is frequently used for measurements of bolometer threads and other small objects.

7. There have been made at the Observatory shop during the year, in addition to such repairs as were required, the following pieces of apparatus:

a. Bearing for circle shaft to insure greater accuracy of motion.

b. A mounting for oblong plane mirror and prism to form an auxiliary fixed-arm spectroscope. This piece of apparatus was used in the determination of the change of deviation of rock salt with change of temperature.

c. A special rheostat for balancing the bolometer, provided with a slide wire operated mechanically from without, and all inclosed by a water jacket.

8. It was shown that the circle of the spectrometer moved less accurately than was desired, and that the error arose in the action of the worm-and-wheel mechanism, which connects it with the clock. Messrs. Warner and Swasey undertook the task of replacing the worm and wheel-segment in use, by others of the desired degree of accuracy. In this they were successful, and the degree of accuracy attained may be inferred when it is said that it is required that the position of the circle shall not be in error by more that 0.5 second of arc, which corresponds to a linear distance of 0.00003 inch on the circumference where the worm and wheel-segment is applied.

9. A comparator for the measurement of bolographs in ordinates and abscissæ was procured of Warner & Swasey. The specifications were prepared at the Observatory with a provisional design which was elaborated and modified by the makers. 10. The large Zeiss photographic lens has been fitted with a Prosch rapid shutter. 11. A new motor and a set of small taps and dies have been added to the shop equipment.

12. On the recommendation of Dr. Kayser, of the University of Bonn, who inspected the Observatory during a visit to this country, sulphuric acid has been used to dry the

spectrometer chamber in the place of lime, as heretofore. A lead tank about 6 feet long and 15 inches wide is supplied with about a gallon at a time of crude sulphuric acid. This acid will abstract more than an equal volume of water from the air before requiring changing, and its use has been attended with very satisfactory results in preserving the faces of the rock-salt optical apparatus.

GENERAL ALTERATIONS.

The Observatory has received necessary repairs, and has been repainted. Its color is now a light drab, and the roof is white in place of the previous brown. It is found that the difference of the temperature maxima of thermometers within and without the Observatory has become nearly 4o C. greater since the repainting. This greatly ameliorates the condition of the observers.

It is proposed to introduce a system of cooling by ammonia gas, to be regulated automatically, so that the apparatus can be maintained through the months of April, May, June, July, August, September, and October, as in the winter, at a standard, constant temperature. As much of the clear observing weather comes in these months, much is hoped from this change.

PERSONNEL.

Mr. L. E. Emerson closed his period of service at the Observatory July 1, 1897.

SUMMARY.

I may sum up the result of the year's work by saying that the positions of between 200 and 300 lines in the infra-red solar spectrum have been accurately established; that an account of the researches of the observatory has been prepared for publication; and that the instrumental equipment has reached a state of excellence never before equaled.

Respectfully submitted.

C. G. ABBOT,

Aid Acting in Charge, Astrophysical Observatory.

Mr. S. P. LANGLEY.

Secretary of the Smithsonian Institution.

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APPENDIX VI.

REPORT OF THE LIBRARIAN FOR THE YEAR ENDING JUNE 30, 1897.

SIR: I have the honor to present herewith a report upon the operations of the library of the Smithsonian Institution during the fiscal year ended June 30, 1897. The entry numbers of accessions to the Smithsonian deposit at the Library of Congress extend from 339,340 to 364,972.

The following table gives an analysis, in volumes, parts of volumes, pamphlets, and charts, during the year:

Publications received between July 1, 1896, and June 30, 1897.

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In addition to this there have been added to the Secretary's library, office library, and the library of the Astrophysical Observatory, 332 volumes and pamphlets, and 2,044 parts of volumes, making a total of 2,376, and a grand total of accessions for the year of 35,912 volumes, parts of volumes, pamphlets, and charts.

These accessions show a gain of 992 in volumes, parts of volumes, and charts over the previous year, and in the number of entries, 793.

The following universities have sent complete sets of their academic publications, including inaugural dissertations:

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While it is not possible to specify the large number of academies, learned societies, editors of periodicals, and private persons who have sent their publications to the Institution, one gift is deserving of especial notice, that of Mr. S. Patcanof, of St. Petersburg. Mr. Patcanof presented over 300 volumes, including manuscripts, printed books, and pamphlets, relating to oriental and Russian philology, archæology, geography, and folklore, and more especially works relating to Armenian literature. The collection includes quite a number of rare works.

Several months were spent in revising the list of foreign establishments to which Smithsonian publications were being sent. It was found that many of them were not sending an adequate return, and a systematic correspondence has been begun with a view to remedying this state of affairs.

A check list of scientific periodicals in the Smithsonian library is being prepared for the new edition of Dr. Bolton's Bibliography of Scientific Periodicals, to be issued by the Institution. In view of the very large number of publications of this character belonging to the Institution, the preparation of this list entails much labor and is not yet completed.

In accordance with the plan of the Secretary for increasing the library exchanges, 673 letters were written for new exchanges and for completing series already in the library, with the result that 104 new exchanges were added to the list and 101 defective series were either completed or added to as far as the publishers could supply the missing parts.

I have little doubt but that much more could be done in this direction if more assistance could be had. The preparation and revision of lists and the examination of the library records for the ascertainment of missing parts requires much and careful labor, and must necessarily proceed slowly. The time occupied in writing the letters is but trifling, compared with that required for the preliminary work. During the year I attended two meetings of the American Library Association-one at Cleveland, in August, 1896, at which I presented a paper entitled "Fifty years of library promotion at the Smithsonian Institution," and at the meeting of the same association held at Philadelphia in June, 1897, a paper on the proposed "International Catalogue of Scientific Literature."

Respectfully submitted.

Mr. S. P. LANGLEY,

Secretary of the Smithsonian Institution.

CYRUS ADLER, Librarian.

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