shows considerable inequalities which must be due to errors of division; these irregularities are visible with the naked eye, two successive divisions differing occasionally by almost ten per cent in length. This irregularity renders an accurate comparison somewhat difficult.

The comparisons were made in a horizontal trough, containing a large quantity of water, the temperature of which was kept slowly rising by means of an electric current. It is not necessary to enter here into all the precautions taken to secure accuracy, as they are all well known to those accustomed to similar work. The readings having been taken in a horizontal position, it was necessary to find experimentally the pressure corrections necessary to reduce the indications to the vertical. Two sets of observations were made; in the first of these Joule's instrument was compared directly with a thermometer made by Tonnelot, divided into tenths of a degree and carefully calibrated by the Bureau International. By means of this instrument Joule's scale value can be directly brought into relationship with M. Chappuis' air thermometer. The second thermometer used in the comparisons was made by Baudin,; it had a more open scale than the Tonnelot, being divided into fiftieths of a degree. The Baudin and Tonnelot had been most carefully compared with each other by Mr. Gannon and myself in the course of another investigation.

First Series. The Tonnelot and Joule A were compared at 19 different temperatures between 7° and 30°. The observations between 13° and 22° were reduced by the method of least squares with the following result.

If t; means a temperature interval on the Joule thermometer reduced by means of Joule's factor and to the corresponding interval on the Tonnelot thermometer, all corrections having been applied, it is found that

Hence the interval in the thermometer A as reduced by Joule is larger than that measured on the Tonnelot instrument by about one part in a thousand.

Second Series. Twenty-two comparisons were made between 14° and 20°, each comparison involving a considerable number of readings. Calling to the interval as measured on the Baudin thermometer

The relation between the Tonnelot and Baudin scale was found to be

making the Joule scale agree exactly with the scale of the French hard glass thermometer.

With respect to the difference in the results obtained in the first and second series, it is to be observed that, owing to the inequality of the divisions, we can hardly trust the Joule thermometer to give us readings which for an interval of 10° are accurate to one part in a thousand. In the second series an attempt was made to eliminate the errors of division as much as possible by taking a great number of readings in the same region, but not within the same two divisions. The second series is more to be relied upon also for the reason that it was made when considerable experience had been gained in the comparison of thermometers. attach therefore much less importance to the second series, and believe that for all practical purposes we must take the scale value of Joule's thermometers to be identical with that of the Tonnelot instrument.

We may now reduce Joule's equivalent to the air thermometer of the Bureau International des Poids et Mesures, and then find

Equivalent as given by Joule in terms of water

at 60° F. and the latitude of Greenwich... 772:55 Reduced to Chappuis' nitrogen thermometer... 77465 hydrogen thermometer.. 77494

Rowland, who has contributed much to the improvement of the science of thermometry, and who is also the author of a very important determination of the equivalent of heat has reduced all his measurements to an air thermometer of his own construction. Having sent one of his thermometers to Dr. Joule, a comparison was made by the latter, which brings Joule's scale into common relation with Rowland's air thermometer. We possess no information as to how the comparison was made, but, accepting it as correct, it would be allowable to draw the conclusion that Rowland's equivalent, if referred to M. Chappuis' nitrogen thermometer, should be reduced by about one unit, so that at 15° C. it would have a value of about 777'3 as against 775 found by Joule.

Ordinary Meeting, February 5th, 1895.

EDWARD SCHUNCK, Ph.D., F.R.S., F.C.S., Vice-President, in the Chair.

The thanks of the members were voted to the donors of the books upon the table.

Mr. R. E. CUNLIFFE and Mr. WILLIAM THOMSON, F.R.S. Ed., were appointed Auditors of the Society's accounts for the current year.

Reference was made to the deaths of three of the Society's honorary members, Professor ARTHUR CAYLEY, the Rev. T. P. KIRKMAN, and Sir JAMES COCKLE, all eminent mathematicians.

The following letter from the President, Mr. HENRY WILDE, F.R.S., was read to the members :

To the Council of the Manchester Literary and Philosophical Society.

Nearly ten years have elapsed since funds were raised by the Society to provide further accommodation for its constantly increasing library and for some structural improvements in the Society's house. It was considered at the time that the enlargement of the Society's premises would serve to accommodate other kindred societies, and thereby lessen the burden of additional expense of maintenance thrown upon the Society by these extensions. The expectation of increased income from this source has not, however, been realised to the extent anticipated; and the falling-off in this revenue, together with a gradual diminution of income from other sources, must at no distant period land the Society in grave financial difficulties. Now that Manchester has become an important seat of learning, through the foundation of

its noble Collegiate institutions, the reason for the existence of this Society appears to me as great, if not greater than it ever was. Numbers of men of high attainments and great mental ability are gathered round this great centre of industry, whose love of literature and science is unquenched by the absorbing business of life, and for whom the problems of nature are an ever-abiding interest. It is for such amateurs in various departments of knowledge, and the professors of academic institutions, that this Society affords a common ground for literary and philosophical research, as well as for pleasant social intercourse. While the aims and objects of the Society are sufficiently high to prevent its seeking any kind of patronage from men in high public or social positions, it has always given a welcome to such as desire to be enrolled among its members. It may be of interest for some of these to know that the Society's roll of ordinary members contains, with few exceptions, the names of all the noblest and best of those who have been identified with the public life and development of Manchester for more than a century; and its honorary members during the same period have made the world famous by their discoveries in every department of science. With the object of maintaining the high character which the Society has so long held in the estimation of the scientific world, and to increase still further its means of usefulness, I now propose to endow the Society with the sum of eight thousand pounds (£8,000) for investment, the annual income arising therefrom to be devoted to the furtherance of the purposes of the Society.

Alderley Edge, February 2nd, 1895.

(Signed)

HENRY WIlde.

It was announced that the Council had gratefully accepted Mr. WILDE's proposal, and

It was moved by Mr. MARK STIRRUP, F.G.S., seconded by Mr. WILLIAM THOMSON, F.R.S. Ed., and resolved, "That the grateful thanks of the members present be accorded to Mr. WILDE for his munificent gift."

Professor H. B. DIXON, F.R.S., gave an account of an examination of the spectrum of the newly discovered atmospheric substance, argon, at the Owens College.