Experiments were made with a spare Barograph belonging to the Meteorological Committee, in order to ascertain the amount of optical distortion, if any, produced by the lenses.

Waxed paper for photographic purposes has been supplied to the Meteorological Office (3 reams), to the India Office (1 ream), and to the Radcliffe Observatory (ream).

Instruction in the use of magnetical or meteorological instruments has been given to the following gentlemen :

Dr. E. van Rijckevorsel in magnetical work.

Nav. Lieut. Dixon, R.N., H.M.S. 'Nassau,' in magnetical work. Staff Comr. Creak, R.N., made observations with a Fox's Circle for H.M.S. Challenger,' and with a Fox's Circle for H.M.S. Nassau.'

Capt. Evans, C.B., F.R.S., made some observations with a magnetometer constructed after his own design.

Photographs of the portable magnetic instruments, of the most approved patterns, have been taken for the use of persons seeking information.

In the month of May a request was received from Col. J. T. Walker, F.R.S., Superintendent of the Great Trigonometrical Survey of India, through the Chairman of the Committee, for provision to be made at the Observatory for vibrating pendulums.

In the year 1865 two pendulums lent by the Royal Society for use in India had been vibrated at Kew by the late Capt. Basevi; and it was necessary that these pendulums should be vibrated again on their return, and that at the same time two pendulums obtained from the Imperial Academy of Sciences at St. Petersburg should also be vibrated.

The Committee at once complied with the request; and at the expense of the Indian Government preparation was made for the experiments in the south hall on the basement story, by removing for a time the apparatus for testing sextants, and building up from the foundation-arches two solid isolated supports for the Russian clock and pendulum.

Capt. Heaviside, R.E., the officer charged with the duty of making the pendulum experiments, arrived in England in July, and, finding all the arrangements satisfactory, at once commenced his experiments, which are still in progress.

Endeavours were made, in connexion with the arrangements just mentioned, to obtain an electrical time communication between Kew and the Royal Observatory at Greenwich; but the proposal failed of

success.

Instruments.-The Kew Standard Barometer, Newman 34, has been cleaned by Messrs. Negretti and Zambra.

In January a new Minimum Thermometer by Casella was obtained to replace the old instrument, which had been accidentally broken.

The several pieces of Mechanical Apparatus, such as the Whitworth Lathe and Planing Machine, procured by Grants from either the Govern

ment Grant Fund or the Donation Fund, have been kept in thorough order; and many of them are in constant use at the Observatory.

A supply of filled thermometer-tubes, of various ranges, has been procured for ultimate graduation as required.

The Committee have, through their Hon. Secretary Mr. Scott, who was present at the Meteorological Congress at Vienna in the month of September, as one of the Delegates from this country, professed their readiness to graduate standard thermometers for any of the Continental observatories which may require them, on condition that the tubes supplied for graduation are sufficiently old.

Library. The usual Donations of English and Foreign Scientific Publications have been received, and a few standard works purchased. Staff-The Staff employed at Kew is as follows:-Mr. Samuel Jeffery, Superintendent; G. M. Whipple, B.Sc., First Assistant; T. W. Baker, Second Assistant; A. J. Rigby, J. E. Cullum, J. Foster, F. Figg, E. Constable.

Note.-Mr. F. J. Page resigned his appointment in January, and B. Bensted was appointed as Junior Assistant. This gentleman has also left, and his place has been filled by E. Constable.

In accordance with a precedent established by the Kew Committee of the British Association, by a Resolution passed in October 1867, Mr. B. Loewy was employed to give instruction to the Assistants. The present Committee, in March last, resolved to resume this practice, and Mr. G. M. Whipple was appointed to give a course of instruction in Mathematics; and he commenced his Lectures in April.

Mr. Robert H. Scott, F.R.S., continues to act as Honorary Secretary to the Committee.

Visitors. The Observatory has been honoured during the year by the presence of several scientific men of eminence. Among these may be

mentioned:

Prof. R. B. Clifton, F.R.S., Oxford.

B. F. Craig, M.D., Army Medical Museum, Washington.

Prof. Felix Klein.

Dr. Radcliffe.

R. Bowie Walcott, M.D., Inspector of Hospitals, Barbados.

Baron von Wrangel, Hydrographic Department for the Black-Sea Imperial Russian Navy.

107 10 5

5 3 2

649 7 6

Night Observations.

Ice

December 11, 1873.

JOSEPH DALTON HOOKER, C.B., President, in the Chair.

Notice was given that at the next Meeting the Right Hon. Edward Cardwell would be proposed for election and immediate ballot.

The President announced that he had appointed as Vice-Presidents :-

The Treasurer.

Sir George Biddell Airy,
Prof. A. C. Ramsay,

Dr. Sharpey,

Major-General Strachey.

Dr. John Beddoe was admitted into the Society.

The following communications were read :—

I. "A Quantitative Investigation of certain Relations between the Gaseous, the Liquid, and the Solid States of Water-Substance." By Professor JAMES THOMSON, LL.D., Queen's College, Belfast. Communicated by Sir WILLIAM THOMSON, LL.D., F.R.S. Received June 20, 1873.

In two communications made by me to the British Association at its Meetings at Edinburgh in 1871, and at Brighton in 1872, and printed as abstracts in the Transactions of the Sections for those years, considerations were adduced on relations between the gaseous, the liquid, and the solid states of matter. The new subject of the present paper constitutes a further development of some of those previous considerations; and a brief sketch of these is necessary here as an introduction for rendering intelligible what is to follow.

Taking into consideration any substance which we can have in the three states, gaseous, liquid, and solid, we may observe that, when any two of these states are present in contact together, the pressure and temperature are dependent each on the other, so that when one is given the other is fixed. Then, if we denote geometrically all possible points of temperature and pressure jointly by points spread continuously in a plane surface, each point in the plane being referred to two axes of rectangular coordinates, so that one of its ordinates shall represent the temperature and the other the pressure denoted by that point, we may notice that there will be three curves--one expressing the relation between temperature and pressure for gas with liquid, another expressing that for gas with solid, and another expressing that for liquid with solid. These three curves, it appears, must all meet or cross each other in one point

of pressure and temperature jointly, which may be called the triple point*.

The curve between gas and liquid, which may be called the boiling-line, will be a separating boundary between the regions of the plane corresponding to the ordinary liquid and those corresponding to the ordinary gaseous state. But by consideration of Dr. Andrews's experimental results (Phil. Trans. 1869), we may see that this separating boundary comes to an end at a point of temperature and pressure which, in conformity with his language, may be called the critical point of pressure and temperature jointly; and we may see that, from any liquid state to any gaseous state, the transition may be gradually effected by an infinite variety of courses passing round the extreme end of the boilinglinet.

The accompanying figure serves to illustrate these considerations in reference to transitions between the three states, the gaseous, the liquid, and the solid. The figure is intended only as a sketch to illustrate principles, and is not drawn according to measurements for any particular substance, though the main features of the curves shown in it are meant to relate in a general way to the substance of water, steam, and ice. A X and A Y are the axes of coordinates for temperatures and pres

* In making this statement, that it appears that the three curves must all cross each other in one point, I would wish to offer it here (as I previously did in the 1871 BritishAssociation paper) subject to some reserve in respect of conditions not yet known with perfect clearness and certainty. I have to suggest that we might not be quite safe in assuming that, within a cavity containing nothing but pure water-substance partly gaseous, the melting temperature and pressure of ice solidified from the gaseous state would be the same as the melting temperature and pressure of ice frozen from the liquid state, and in making other suppositions, such as that the same quantity of heat would become latent in the melting of equal quantities of ice formed in these two ways, and in neglecting conceivable but, I presume, as yet imperfectly known distinctions of capillary conditions between ice amply wet with water and ice only moistened with the last vestiges of water before the whole liquid may be either evaporated or frozen. It might be a question in like manner whether we can be sure that there can be theoretically a condition of repose in a cavity containing only perfectly pure water-substance in which the three states are present together, each in contact with the other two, so that there would be ice partly wet with water, and partly dry in contact with gaseous water-substance, or steam as it may be called, while the water and steam were also in contact with each other. I offer these remarks by way of caution, as they force themselves into notice when we attempt to sketch out the features of the three curves under consideration, and because they may serve to suggest questions for experimental and theoretical investigation which may have been generally overlooked before. In the present paper, however, I proceed on assumptions, such as are usually tacitly made, of identity in the thermal and dynamic conditions of pure ice solidified in different ways, assumptions which, so far as is known, may be, and probably are, perfectly true; and I proceed on the supposition that there can be theoretically the condition of repose here alluded to, of the solid, liquid, and gaseous states, present together each in contact with the other two-and consequently that the three curves would meet or cross each other in one point, which I have called the triple point.

† Mention of this condition has been already made in a former paper by me in the 'Proceedings of the Royal Society,' November 16, 1871, page 2.