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Electrograph.-This instrument has been in almost continuous action through the year under the care of Mr. Harrison. Certain improvements in minor details, suggested by Sir W. Thomson, have been introduced from time to time.

It has been thought desirable to make a determination of the scale value of the instrument throughout the whole extent of its range. The Committee not possessing a sufficiently powerful battery for the purpose, the Electrometer was conveyed at Mr. De La Rue's suggestion to his Laboratory, where a complete determination of its scale value was made over the range of tension afforded by 1,200 chloride of silver cells. A detailed account of the experiment was afterwards laid before the Royal Society, and printed in the "Proceedings," vol. xxvii, p. 356.*

At the request of Professor Mascart, a typical set of curves, illustrating the action of the Electrograph during different kinds of weather, was reduced and engraved by the Pantagraph at the Meteorological Office, and forwarded for his use in illustration of the lectures he delivered before the Société Météorologique de France.

These engravings have since been reproduced, together with notes respecting the instrument, in a Report on Atmospheric Electricity, drawn up by Professor Everett, for the Permanent Committee of the Vienna Congress, which is about to be published by the authority of the Meteorological Council.

The late Captain R. G. Scott, R.E., and since his decease, Captain R. Y. Armstrong, R.E., visited the Observatory and inspected the working of the instrument with the view of possibly utilizing the Electrometer in the study of atmospheric electricity at the various torpedo stations round the coast.

Two Electrographs, similar in construction to the instrument at Kew, have been constructed by Mr. White, of Glasgow, and after examination at the Observatory, forwarded, the one to the Brussels Observatory, the other to Zi-ka-Wei, China.

Photoheliograph. -The re-examination of the measurements of the Kew sun-pictures, as noticed in former Reports, has been steadily carried on throughout the year by Mr. Whipple, assisted by Mr. M'Laughlin, who has been temporarily engaged for this purpose.

During the year upwards of 400 pictures have been measured, and it is hoped that the end of the series will be reached in the early

months of 1879.

* With the view of rendering the indications of the instrument better adapted for treatment with the Harmonic Analyser, it is in contemplation to somewhat alter the existing bifilar suspension of the needle, and at the same time to adopt the new insulating stand devised by Professor Mascart (“ Nature,” vol. xviii, p. 44) which will be substituted for the present supports of the water reservoir. These changes may cause a short discontinuity in the observations.

Mr. Marth is still engaged on the reduction to heliocentric elements of the pictures for 1864 to 1868 inclusive.

All of these operations have been conducted under the direction and at the expense of Mr. De La Rue.

The eye-observations of the sun, after the method of Hofrath Schwabe, have been made daily, when possible, as described in the Report for 1872, in order for the present to maintain the continuity of the Kew record of sun-spots.

Extra Observations.-The Solar-radiation Thermometers are still observed daily, and a new form of the instrument designed by Professor G. C. Foster, is at present undergoing trial.

The question of observing Solar Radiation having been referred by the Meteorological Council to the Kew Committee, a sub-committee has been appointed to take the whole subject into consideration.

The Campbell Sundial described in the 1875 Report, continues in action, and the improved form of the instrument, giving a separate record for every day, of the duration of sunshine, has been regularly worked throughout the year and its curves tabulated.

A paper comparing the relative amount of sunshine recorded by this instrument during the year 1877, with the amount registered at the Royal Observatory, Greenwich, by a similar apparatus, has been read by the Superintendent before the Meteorological Society, and published in their Quarterly Report, vol. iv, No. 28. It shows that the difference in the total duration of sunshine observed at the two stations, which amounted to 171 hours in the year, was in great measure due to the preponderance of westerly winds, which carry the smoke of the metropolis over the Royal Observatory.

A copy of the Kew instrument, constructed by Mr. Browning for the Brussels Observatory, has been compared at the Observatory; and another instrument, with a new form of mounting, designed by Mr. R. J. Lecky, F.R.A.S., is at present being tried.

Wind Component Integrator.-This instrument, at the time of the last Report, was working temporarily, attached to the Kew Anemograph. This arrangement was found, however, to interfere with the regular action of the latter instrument, and accordingly its own cups and vane, sent over by Professor von Oettingen, have been fitted to it by Mr. R. W. Munro; and with the exception of a small period, during which it was under repair (one of the cups having been carried away by a high wind), it has been in good action. A comparison of its indications with those of the ordinary instrument will shortly be made.

Photo-nephoscope. This instrument, designed by Professor Stokes and Mr. F. Galton for the purpose of photographing clouds at the time of their passage across the zenith, has been the subject of experiment for some time, with a view of its adoption as a means of trigo

nometrically determining the height of clouds. The experiments are

still in progress.

Verifications. The Committee have to report that the work of this department of the Observatory is still increasing, and its field extending, the makers who send instruments for examination, from places both at home and abroad, is continually becoming more

numerous.

The following magnetic instruments have been verified, and had their constants determined :

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A set of Magnetographs for the Brussels Observatory.

A Unifilar for Messrs. Negretti and Zambra.

A Unifilar for the Dutch Arctic Expedition.

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Two Azimuth Compasses for Mr. H. M. Stanley.

A Dip-circle for the Austro-Hungarian Government.

There have also been purchased on commission and verified:—a Unifilar and Dip-circle for the Marine Observatory, San Fernando, Spain; a pair of Dipping-needles for Professor Wild, St. Petersburg; a Unifilar, Dip-circle, and Fox Circle for Captain Carl Wille, Horten, Norway; a Dip-circle for Senhor Capello, Lisbon Observatory. There are also now undergoing verification a Dip-circle for Lieutenant van Hasselt; a Dip-circle for the Austro-Hungarian Government; a Unifilar, Dip-circle, and Fox Circle for Professor Greene.

Two Sextants have been verified.

The following meteorological instruments have been verified, this portion of the work being entrusted to Mr. T. W. Baker, assisted by Messrs. Foster, Constable, and Gunter:

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In addition, 134 Thermometers have been tested at the meltingpoint of mercury.

14 Standard Thermometers have been calibrated and divided. The following miscellaneous instruments have also been verified :—

Hydrometers...
Anemometer

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A Barograph and Thermograph have been examined, and their scale values determined, for the Brussels Observatory; also a similar pair of instruments for the Zi-ka-Wei Observatory, and a Thermograph for the Japanese Government.

There are at present in the Observatory undergoing verification, 19 Barometers, 182 Thermometers, 4 Anemometers, and 1 Raingauge.

A number of Aneroid Barometers, of a new pattern, have been received from MM. Hottinger and Co., of Zürich, for comparison.

The "Hall Mark," figured in last report, has been etched, at the desire of the makers, upon a number of the Thermometers compared at the Observatory.

A Hydraulic Press especially constructed for the purpose of subjecting Deep sea Thermometers to pressures similar to those they experience when suuk to great depths, has been erected in the workshop, by Messrs. Hopkinson and Cope. It is capable of exerting a strain equal to 4 tons on the square inch. Several protected Thermometers have been found to stand this test successfully.

Air Thermometer.-The Committee are taking steps to obtain a standard air thermometer.

The old "Royal Society" Standard Barometer, with the flint and crown-glass tubes refilled by Negretti and Zambra, has been compared with the Kew standard daily for several months. Its scale has also been measured and its error determined.

Comparison of Standard Barometers.-The account of the comparison of the Standard Barometers at Greenwich and Kew, which resulted in proving a close agreement between the standards of the two Observatories, was published in the "Royal Society Proceedings," vol. xxvii, p. 76.

With a view to determine the source of small variations in the correction to the working standard of the Observatory (Newman 34) and the large Welsh's standards, numerous comparisons have been made between the instruments, from time to time, but as yet without

success.

Professor B. Stewart has had similar series of readings made between the Owens College ordinary Standard Barometer and one after the Kew model, also filled by Welsh's system. The results tend to show a most close agreement between the two forms of instru

ment.

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For a complete account of these experiments, see Manchester Philosophical Society's Proceedings," vol. xvii, No. 10.

Freezing Point of Water.-In consequence of a communication from Dr. Guthrie as to the presence of cryohydrates in water lowering its freezing point, a series of experiments was made for determining the melting point of distilled-water ice, rainwater ice, clean pond ice, and the commercial ice used at the Observatory. It was found to be practically identical in all the specimens examined, the differences observed only amounting to a few hundredths of a degree Fahrenheit. Waxed Paper, &c., supplied.-Waxed paper has been supplied to the following Observatories:

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A supply of chemical and photographic material has also been procured for the Coimbra Observatory.

A set of lamps, for use with Magnetographs, has been supplied to the Mauritius Observatory.

Loan Exhibition.-The old instruments (with the exception of a Magnet, the property of the Royal Observatory, Greenwich, and a Unifilar Magnetometer) lent to the Science and Art Department, enumerated in the Report for 1876, remain for the present deposited in the galleries at South Kensington.

A Dip-circle, the property of Mr. Dover, has been withdrawn from the collection.

Workshop. The several pieces of Mechanical Apparatus, such as the Whitworth Lathe and the Planing Machine, procured by Grants from either the Government Grant Fund or the Donation Fund, for the use of the Kew Observatory, have been kept in thorough order, and many of them are in constant, and others in occasional use at the Observatory, but the funds of the Committee do not at present allow of the employment of a mechanical assistant, although one is much needed. Library. During the year the Library has received, as presents, the publications of

11 English Scientific Societies and Institutions,

43 Foreign and Colonial Scientific Societies and Institutions.

Ventilation Experiments.-The Sanitary Institute of Great Britain having applied to the Committee for permission to use the experimental house (which was unoccupied at the time) for a series of experiments on the ventilating powers of cowls of different form, the Committee granted it, and a large number of observations were made by them, extending over several weeks. A second set, with other appliances, is now about to be instituted.

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