An attempt has also been made to apply the Gaussian analysis to sudden magnetic disturbances, and, with a view to their application in future work, the values of the Gaussian coefficients have been obtained for twenty different observatories, and the numerical equations formed for the elements of magnetic force in three directions mutually at right angles, and also the equation for the magnetic potential in terms of the Gaussian constants to the fourth order. The observatories of Washington and Los Angeles in the United States of America are included in this list.

During the past year a very interesting volume has been published, giving the magnetic observations at the United States Naval Observatory at Washington for 1888 and 1889. In accordance with the recommendation made at the International Conference held at Washington in 1884 the hours adopted in these American tables are for the seventy-fifth meridian (west of Greenwich), mean time.

The results of the Washington observations are contained in ten tables, as follows:

TABLE I.-Mean hourly values of declination for 1888-89.

TABLE II.-Mean hourly declination for each month of 1888-89, taken from monthly composite curves.

TABLE III. Mean hourly values of horizontal force for each month of 1889 in c.g.s. units (dynes).

TABLE IV. Mean hourly values of vertical force for each month of 1889 in c.g.s. units (dynes).

TABLES V., VI., and VII.-Hourly values of declination, horizontal force, and vertical force respectively.

TABLE VIII.-Summary of disturbances in declination during 1888-89, determined from the composite curve.

TABLES IX. and X.-Observations for 1888-89 for horizontal force and dip respectively.

In addition to the tables there are fourteen plates as follows:

PLATE I. Examples of the daily photographic traces of declination, horizontal and vertical force.

PLATE II.-Mean diurnal variation of the magnetic elements for 1889.

PLATES III., IV., V., VI.-Monthly composite curves of declination for 1888 and 1889, each plate for six months.

PLATES VII. to XIV.--Comparisons of disturbed days of declination at Washington, Los Angeles, Toronto (Canada), and Pawlowsk (St. Petersburg).

The traces are all placed for the same time, and are reduced to the same length of base line. In the horizontal-force trace increase of ordinate denotes increase of force, and in the vertical-force trace increase of ordinate denotes decreasing force, and the scale-value adopted for both horizontal and vertical force instruments is very nearly the scale-value recommended in the third report of this committee to the British Association (1887), viz., 1 centimetre of ordinate=0005 c.g.s. units.

The Committee entertain hopes that another of their recommendations, to which attention was first drawn in their third report (1887), and to which attention was again drawn in their fifth and sixth reports, viz., the establishment of a Magnetic Observatory at the Cape of Good Hope, is about to be carried out. At a meeting of the Committee held on June 2, 1891, at which the Chairman, Sir William Thomson, Professor Rücker, Commander Creak, Mr. Ellis, and Mr. Whipple were present, and at which Mr. Gill also attended at the request of the Committee, a statement was drawn up with regard to the requirements for a Magnetic Observatory at the Cape of Good Hope, and a rough estimate of cost and maintenance

was supplied by Mr. Whipple at the request of the Committee. It was resolved to ask the First Lord of the Admiralty to consider a statement of these requirements and to receive a deputation of the Committee and other scientific men interested in the progress of terrestrial magnetism to urge the establishment of a Magnetic Observatory at the Cape of Good Hope, to be placed under the direction of Mr. Gill, the Director of the Cape Royal Astronomical Observatory. In answer to Sir William Thomson's application to the first Lord of the Admiralty, asking him to receive a deputation on the subject, the First Lord requested that before receiving a deputation he might have a statement of the requirements with regard to the proposed magnetic observatory at the Cape to be asked for by the deputation.

At the request of Sir William Thomson a statement was laid by the Chairman of the Committee before the first Lord of the Admiralty, pointing out the importance of establishing a magnetic observatory at the Cape of Good Hope and submitting a rough estimate of the cost of observatory and apparatus and the necessary requirements.

In a circular issued by the International Meteorological Committee, which will meet in Munich in September next, the following questions bearing on terrestrial magnetism are proposed for consideration:--

QUESTION 8.-Is it not necessary in the introduction to the publication of magnetic observations to give the absolute values of the normal readings of differential instruments?

QUESTION 31.-Would it not be useful to come to an agreement as to the values of the coordinates of magnetic curves registered by magnetographs?

To these questions, according to the opinion of this Committee, as expressed in their reports, especially in their third report (1887), there can be but one answer. The absolute values of the normal readings of all magnetic instruments and their scale-values should be given in the publication of magnetic records, and it would be convenient that the same scale-values should be adopted at all Observatories for similar instruments. The value recommended by this Committee for changes of horizontal and vertical force is 0005 c.g.s. units for 1 centimetre of the scale.

The Committee recommend that for self-registering magnetographs the scale values for declination, horizontal force, and vertical force should be arranged so that equal changes of ordinate correspond to equal increments of absolute force in three directions at right angles to one another, dr, dy, and 8z being the changes in the horizontal force in the magnetic meridian, the horizontal force perpendicular to the magnetic meridian and the vertical force respectively.

The Committee also recommend that as far as possible the same timescale should be adopted for the registering magnetographs at different Observatories, and that this scale should be 15 millimetres to the hour.

Professor Lemström, of Helsingfors, also suggests the following questions for consideration:

QUESTION 29.-What method should be employed for the study of earth-currents? QUESTION 30.-What is the extent of our knowledge of atmospheric electricity, and how should we measure it quantitatively so as to get better results?

QUESTION 32.-What instrument is best for studying the variations of vertical intensity of terrestrial magnetism?

With regard to Question 32 the Committee are of opinion that Lloyd's vertical-force magnetometer is a very satisfactory instrument for studying the changes in the vertical magnetic force.

Report of the Committee, consisting of Professor G. CAREY FOSTER, Sir WILLIAM THOMSON, Professor AYRTON, Professor J. PERRY, Professor W. G. ADAMS, Lord RAYLEIGH, Dr. O. J. LODGE, Dr. JOHN HOPKINSON, Dr. A. MUIRHEAD, Mr. W. H. PREECE, Mr. HERBERT TAYLOR, Professor EVERETT, Professor SCHUSTER, Dr. J. A. FLEMING, Professor G. F. FITZGERALD, Mr. R. T. GLAZEBROOK (Secretary), Professor CHRYSTAL, Mr. H. TOMLINSON, Professor W. GARNETT, Professor J. J. THOMSON, Mr. W. N. SHAW, Mr. J. T. BOTTOMLEY, and Mr. T. GRAY, appointed for the purpose of constructing and issuing Practical Standards for

use in Electrical Measurements.

THE work of testing resistance coils at the Cavendish Laboratory has been continued. A table of values found for the coils is appended :

Among these the coil B.A. No. 38 No. 77 has a special interest ; it is an original platinum silver coil which formerly belonged to Professor Balfour Stewart, and is now in the possession of Professor Schuster at the Owens College. According to the label on it, it was right at 16°.5. According to the Secretary's observations, its value is one mean B.A. Unit at 14.9. This coil, therefore, would appear to have risen in value since about 1867 by 0006 B.A.U., and this result is not in accordance with the conclusions deduced in 1888 from the observations on the other platinum silver coils then examined.

Some further experiments have been made with satisfactory results on the air-condensers of the Association. A megohm resistance box has been purchased for use in comparisons of capacity.

With a view to testing the permanence of the resistance standards it was thought desirable to compare them again with the mercury standards. This was done in December and January by the Secretary. The coil Flat was compared with two mercury tubes constructed in 1884 by Mr. J. R. Benoit, which had been filled at Cambridge early in the year 1885, and had remained full since. An account of the comparison was read before the Physical Society May 9, 1891, and appears in the Philosophical Magazine,' July, 1891.

The tubes were compared with the B.A. standards. If we take, as was done in 1885, for the resistance in B.A. units of a column of mercury 100 cm. long 1 sq.-mm. in section, the value 95412 B.A.U., we have the following results for the resistance of the tubes in Legal Ohms.

The differences are only '00004 Legal Ohms, which is too small to feel really certain about. If we accept for the resistance of mercury the value 95352 B.A.U., which (B.A. Report, 1890) appears the best value, then we have:

These comparisons were made with Flat, and lead to the conclusion that it has remained unchanged.

In November, 1890, the Association was invited by the President of the Board of Trade to nominate two members to represent the Associa tion on a Committee On Standards for the Measurement of Electricity for use in Trade.' A meeting of the Electrical Standards Committee was held on December 2, and it was agreed to suggest to the Council of the Association the names of Professor Carey Foster and Mr. R. T. Glazebrook as representatives. These gentlemen were appointed by the Board of Trade together with Mr. Courtenay Boyle, C.B., Major Carden, Mr. E. Graves, Mr. W. H. Preece, Sir Wm. Thomson, Lord Rayleigh, Dr. Jno. Hopkinson, and Professor Ayrton.

This Committee after various meetings drew up a report, a copy of which is printed as Appendix I. to this report.

The standards of resistance constructed in accordance with Resolution 6 of the report are now in the hands of the Secretary, and are being compared with the standards of the Association.

Numerous experiments on the methods of constructing Clark's cells, and on the electromotive force of such cells, have been made at the Cavendish Laboratory by Mr. Wilberforce, Mr. Skinner, and the Secretary. These are still incomplete, but the experiments so far as they have been finished lead to the value 1·434 volts at 15° for the E.M.F. of the cell. The value found by Lord Rayleigh was 1·435 at the same temperature.

Mr. Fitzpatrick has continued his experiments on the resistance of silver, and an account of these will be given in a future Report.

The Committee ask for reappointment with omission of the names of Principal Garnett and Mr. H. Tomlinson, and addition of those of Dr. G. Johnstone Stoney and Professor S. P. Thompson. They recommend that Professor Carey Foster be Chairman, and Mr. R. T. Glazebrook Secretary. They further ask to be allowed to retain an unexpended balance of last year's grant, amounting to 177. 4s. 6d., as well as for a new grant of 101.

APPENDIX I.

REPORT OF THE ELECTRICAL STANDARDS COMMITTEE APPOINTED BY THE BOARD OF TRADE.

To the Right Honourable Sir Michael Hicks-Beach, Bart., M.P., President of the Board of Trade.

In compliance with the instructions contained in your Minute of the 16th December last, that we should consider and report whether any, and, if so, what action should be taken by the Board of Trade under section 6 of the Weights and Measures Act, 1889, with a view to causing new denominations of standards for the measurement of electricity for use for trade to be made and duly verified, we have the honour to submit the following report:

1. Before coming to a decision as to the points referred to us, we were anxious to obtain evidence as to the wishes and views of those practically interested in the question, as well as of Local Authorities who are concerned in the administration of the Weights and Measures Acts.