The President gave a short historical sketch of the Society on the occasion of the commencement of its Hundredth Session. He said that, before the business commenced, he ought to call attention to a peculiarity of the present meeting, and to make one or two observations upon it. This was the hundredth session of the Royal Society. Most cordially did he congratulate the Society and its members on having arrived at that interesting period of its history. But it was right he should say that it would be a mistake to suppose that, although this was the hundredth session, they were absolutely centenarian. This was not the anniversary of the birth of the Royal Society. For some reason or other–he did not know how–the hundredth session began before the Society was absolutely a hundred years old. How it exactly came about he was not quite sure. The Royal Society's charter bore date March 1783; and he supposed, like other great institutions, they had a previous autumn session–and in that way, possibly, the difference was to be accounted for. But, in any view, it is a great occasion for meditation and observation, and there may come a time for such a word, but on the present occasion he had not the material sufficient to do anything like justice to a theme so large. Only in a few sentences would he go back to March 1783, and glance upon the long career which the Society had run. A long and distinguished course, he thought they might say, seeing it was to their distinguished predecessors. they owed its glory and its present flourishing existence. There had been many speculations as to where the Royal Society came from, and its feeders had been examined and searched for with great assiduity.

The substance of part at least of this paper was given in 1876 as an evening lecture to the British Association at its Glasgow meeting.

While engaged in writing the article “Mechanics” for the Ency. Brit., I had to consider carefully what basis to adopt, and decided that the time had not yet come in which (at least in a semi-popular article) Newton's laws of motion could be modified. The article was therefore based entirely on these laws, with a mere hint towards the end that in all probability they would soon require essential modification. It is well, however, that the question of modification should now be considered; and this should be done, not in a popular essay but, before a scientific society.

In the year 1860, at the meeting of the Social Science Association in Glasgow, I read a paper on “The Causes of Illegitimacy in Scotland,” which was published shortly afterwards; and eleven years later (1871), at the meeting of the British Association in Edinburgh, I read another paper on “The Illegitimacy of Banffshire,” which was privately printed. On the present occasion I intend to confine my observations to the facts exhibited by the Registrar-General's returns.

The following pages contain an account of experiments made by myself and Mr T. Lindsay, at the request of Professor Tait, to determine the absorption of damp air containing a known quantity of water vapour, by finding in what proportions dry air and olefiant gas must be mixed in order that the absorption of the mixture may be the same as that of the damp air. The experiments were made according to the method described by Professor Tait in a letter read by Sir William Thomson at the Southampton meeting of the British Association (see Nature, vol. xxvi. p. 639, 1882). They consist of two series—the first, a series of rough experiments made, first, to determine whether or not the method would work, and, secondly, to find the dimensions of the apparatus which would give the best result; the second, a series of more careful experiments made when the method was found to give satisfactory results.

To test by an independent process the accuracy of the unit of my pressure gauge, on which the estimated corrections for the “Challenger” deep-sea thermometers depend, it was arranged that H.M.S. “Triton” should visit during the autumn a region in which soundings of at least a mile and a half could be had. A set of manometers, filled with pure water, and recording by the washing away of part of a very thin film of silver, were employed. They were all previously tested, up to about 2½ tons weight per square inch, in my large apparatus. As I was otherwise engaged, Professor Chrystal and Mr Murray kindly undertook the deep-sea observations; and I have recently begun the work of reducing them.

The series of observations to be described was undertaken in order to ascertain how far a small pocket spectroscope could be relied upon for the prediction of rain, with a view to its popular use for that purpose.

The instrument employed was Hilger's smallest sized direct-vision spectroscope, its length being one inch and a half, and its diameter half an inch. It was furnished with the ordinary adjustable slit, and had no special provision for the exclusion of dust. It is desirable, however, to use an instrument which has the eyehole protected by a plate of thin glass, and the slit covered with a thicker plate. In this case care must be taken to keep the glass free from scratches, which greatly obscure the spectrum.

The calming effect of oil on troubled waters is so well known and so often referred to, that we might have expected there would, by this time, have been a considerable amount of written information on the subject. This calming effect of oil is not only well known, but it has also become so stereotyped by constant repetition, that it seems to have acquired the stamp of classical antiquity upon it, yet one is surprised to find that reference to it in early writers is strangely conspicuous by its absence. Our knowledge of the subject seems to have lived almost entirely in tradition.

In case you should not have any better account of it from those who keep hourly, or perhaps continuous, observations, you may like to mention to the Society this evening, on no more than my twelve-hour testimony,–the occurrence of a decided meteor, of meteorology, last night.