moting the proposed Exhibition, and appointing official delegates to the Conference.

My best thanks are due to M. Le Play for his kindness towards me during my visit to Paris, and I should fail in my duty were I not to acknowledge with gratitude the care and interest shown by M. De Chancourtois in the promotion of the object of my mission to that great metropolis.

I have the honour to be, Gentlemen,

Your obedient Servant,

Farrar's Building, Temple,
July 1866.

LEONE LEVI.

· Report on the Mural Standard. By JAMES YATES, F.R.S.

I TAKE up the account of the Mural Standard, exhibiting in immediate apposition the Yard and the Metre with their divisions, where I laid it down last year at Birmingham*.

The want of Mural Standards of the linear measures has been shown on the authority,

1st, of the Commissioners for the restoration of the Standards, whose Report, with the evidence, was published by order of Parliament in 1841 (see pp. 16, 17);

2ndly, of G. B. Airy, Astronomer-Royal, in his letter to Lord Monteagle, Comptroller of the Exchequer, dated Feb. 1st, 1859;

3rdly, of Lord Monteagle himself, in his letter transmitting that of Professor Airy to the Secretary of State for the Home Department (see Appendix to the Report quoted below);

4thly, of the Select Committee of the House of Commons on Weights and Measures, A.D. 1862 (see their Report, p. ix).

These Commissioners and public officers all concur in advising that Mural Standards of length should be exhibited in public places, where they may be accessible to the people generally. But, although this subject has been earnestly and repeatedly recommended to the attention of the Government, and although the advice so given is agreeable to the general practice of civilized nations both in Europe and America, yet nothing has been done by our Government to give effect to these recommendations.

Parliament has, however, passed a law, which received the Royal Assent on the 6th instant, and which may be regarded as a first step. The Select Committee of the House of Commons, to which I have alluded, adopted (A.D. 1862) a series of Recommendations, one of which was, "that a Department of Weights and Measures be established in connexion with the Board of Trade." This has been done by the Standards of Weights, Measures, and Coinage Act, 1866, Sections 1, 10, 11, 12. But much remains to be done, and Mr. Ewart, the Chairman of the before-mentioned Select Committee, has accordingly given notice of a motion next Session to reappoint the Committee with a view to facilitate the introduction into this country of the Metric System of Weights and Measures. The task imposed on the Committee will be no less arduous than that which they executed with such distinguished success in the spring of 1862. It will be the duty of those who are friendly to this great improvement to avail themselves of the interval by collecting all kinds of evidence, which may guide the Committee in their determinations; and we trust that they will continue to act in

* See Report of the Birmingham Meeting (Sections), p. 159.

the same liberal and enlightened spirit, and in conjunction with the many able and excellent men, in both Houses of Parliament, whether in or out of office, who now combine their efforts in the same direction. The extensive exhibition and use of our Mural Standard will, as we may confidently anticipate, be among the principal means of accomplishing the object.

The Committee of the British Association, soon after its appointment, thought it desirable to appply for advice and assistance to the Chemical Society, which includes many of the most eminent chemists and metallurgists in the kingdom. Their application was granted in the kindest manner by the President of the Society, Dr. William Allen Miller, the Secretary, Dr. Odling, and the other members of the Council. The subject was brought before the Society at two of its meetings, and the result was a very important change in the course of proceeding. Professor Frankland advised that, instead of Baily's metal, or any other metallic substance, either simple or compound, the Mural Standard should be made of white glazed porcelain. The question was carefully considered, more especially in regard to the durability of porcelain, and its susceptibility of changes by expansion and contraction. With regard to durability, we know from innumerable examples that porcelain will last for hundreds of years without any perceptible decay. We also know that it is very little subject to expansion and contraction from the changes of atmospheric temperature. But it is also well known that all objects made of clay contract by exposure to great heat. How could we pass our porcelain Standard through the ordeal of a furnace without destroying the dimensions marked upon it? In this difficulty we were fortunate in obtaining the assistance of Mr. Casella, Philosophical Instrument Maker to the Board of Ordnance. This gentleman, whose business makes him familiar with works of this particular description, instituted a series of experiments, which proved that a slab of porcelain after completion. contracts visibly on its reexposure to a great heat, but that, if the heat be sufficiently intense and sufficiently long continued, an adequate security will be obtained against future change. Consequently a slab may be prepared by firing at first, and then have the lines etched in with hydrofluoric acid, the figures and letters painted with enamel, the lines rubbed in with the same, and then the lines, figures, and letters all burnt in, after which treatment it will not shrink at all. Having obtained so satisfactory a result, the Committee desired Mr. Casella to proceed with his work.

The Committee have seen no reason to make any important change in the form and dimensions of the instrument. These remain nearly as they were shown to the Statistical Section of the British Association at Birmingham. But, as the Yard was then placed in close contact with the Metre, a question arose whether the two measures might not be more clearly distinguished from each other; and to effect this it was proposed that the Yard should be marked in red lines and the Metre in blue. This suggestion was adopted, and the instrument, thus completed, is thought to be elegant and attractive as well as clear and distinct. If, however, any persons prefer having it marked with black lines this may be done.

It was requisite that the divisions should be so exact that no inaccuracy could be perceived either by the sight or the touch. This has been accomplished by our artist, who obtained from M. Perreaux, of Paris, one of his beautiful dividing instruments, which is so constructed as to divide, if required, to the 500th part of a millimetre, a length far more diminutive than can ever be found necessary. About the tenth of a millimetre is sufficient to answer every useful purpose.

Besides showing the name of the maker on each instrument as a voucher for its accuracy, the Committee hope to obtain the stamp of the Government as directed by Act of Parliament. But as the stamp could not be impressed on the porcelain, a number will be marked and burnt on every instrument, and the same number with the Government stamp will be impressed on the frame.

The price cannot be at present determined. We can only say that it will not exceed £5 5s. When the demand is sufficient the price may be lowered.

Whilst Mr. Casella has been employed upon our Mural Standard, a Birmingham artist, Mr. Gargory, who pursues the same line of business, has produced an instrument which may be called a School Metre, being especially adapted for school use. It is made of wood and ivory. It shows the Metre together with the Yard, both Long and Cloth Measure, the principles of its construction being generally the same with those of the Mural Standard. Its price will be about 7s.

The sum of £50 voted by the British Association at Birmingham having been expended, it will be necessary to ask for a further grant. If the General Committee of the Association should think it proper to send copies of the Mural Standard to all the places where the Association has met, or even to a considerable number of them, a grant of £100 will not be too much; and it may be deserving of consideration, that if philosophers, who are proverbially poor, can afford such a sum as £100, the Lords of Her Majesty's Treasury, who have hitherto expended nothing on this great and indispensable public provision, need not grudge any amount which may be found requisite.

An Account of Meteorological and Physical Observations in Three Balloon Ascents made in the years 1865 and 1866 (in continuation of twenty-five made in the years 1862, 1863, and 1864), under the auspices of the Committee of the British Association for the Advancement of Science, by JAMES GLAISHER, F.R.S., at the request of the Committee, consisting of Colonel SYKES, The ASTRONOMER ROYAL, Lord WROTTESLEY, Sir D. BREWSTER, Sir J. HERSCHEL, Bart., Dr. LLOYD, Dr. ROBINSON, Mr. GLAISHER, Mr. GASSIOT, Prof. TYNDALL, Dr. FAIRBAIRN, and Dr. W. A. MILLER.

Ar the first appointment of the Balloon Committee it was charged with the determination of the law of the decrease of temperature with increase of elevation, as the primary object of research; and some two years since this law seemed to have been pretty well determined, but up to that time the experiments had been, for the most part, made in the months of summer and during the hours of afternoon. The principal duty of the Committee was the verification of the results then found, by including experiments at other times of the day, and at other seasons of the year. It was expected that this part of the work to be done by the balloon would have been completed. In carrying out these experiments, it was found that those taken in the morning hours did not accord with those taken in the afternoon hours, nor did those taken at one time of the year agree with those taken at other times of the year.

In the course of these experiments an accidental descent just at

the time of sunset showed very little or no difference of temperature for a height of nearly half a mile. The question then arose as to whether it was possible that at night the temperature might increase with elevation, and not decrease as always heretofore had been considered, and acted upon whenever such entered into physical investigation.

The Committee last year therefore was reappointed with special reference to night observations at any time of the year made within a moderate distance of the earth. To make day observations, in winter and the adjacent months at any hour in the day; in summer to be made in the morning, only the subject of temperature to be considered as of the first importance, with any other of the usual experiments which might be possible. Up to the Meeting at Birmingham twenty-five ascents had been made, of which seventeen had been made in the months of June, July, August, and September, but not one in May, and mostly during the hours of afternoon.

§ 1. INSTRUMENTS AND APPARATUS.

The instruments were of the same construction as those used in the previous experiments; in addition well-made miners' lamps were used to illuminate the instruments at night.

§ 2. OBSERVING ARRANGEMENTS.

The instruments were in all cases placed on suitable framework, attached to the outside of the car, and sufficiently protected from all effects of radiation.

Circumstances of the Ascents, and General Observations.

Ascent from Woolwich Arsenal, October 2, 1865.-The first ascent after the Meeting at Birmingham was made on October 2nd. The balloon used was that of Mr. Orton, of Blackwall.

When the sun had set for nearly three-quarters of an hour and night had fairly set in, the moon shining brightly, and the sky free from cloud, the balloon left Woolwich Arsenal at 6h 20m, the temperature at the time being 56°. Within three or four minutes a height of 900 feet was reached, and till this time I failed in directing the light of the Davy lamp properly. When I succeeded the temperature was 57° and increasing; on reaching 1200 feet high it had increased to 58°.9; we then descended to 900 feet, and the temperature decreased to 57°.8; on turning to ascend again the temperature increased to 59°6 at 1900 feet high, being 34° warmer than when the earth was left. On descending again the temperature decreased to 57° at the height of 600 feet, and in the several subsequent ascensions and descensions the temperature increased with elevation, and decreased on approaching the earth. On every occasion the highest temperature was met with at the highest point. This result was remarkable indeed. The different degrees of the humidity of the air met with in this ascent are no less remarkable. Considering saturated air as represented by 100, at the commencement of the ascent in the balloon it was 95; at Greenwich Observatory it was 84; towards the end of the ascent in the balloon it was 85, and at Greenwich was 97. The state of things was reversed, and would indicate that the water in the air had fallen. Its amount at the beginning of the ascent was 5 grains in a cubic foot of air, and at the same elevation was 4 grains in the same mass of air at the end of the ascent.

The readings of the instruments were taken very slowly, owing to the difficulty experienced in directing the light properly. I failed in all magnetic experiments, and indeed in nearly all but those relating to temperature and

humidity. Two self-registering minimum thermometers were tied down, one with its bulb resting on cotton-wool, fully exposed to the sky, and the other with its bulb projecting beyond the supporting frame: their indexes were at the end of their columns of spirit on starting, or at 56°. At every examination of each of these instruments a space was found between its index (which remained unmoved) and the end of the column of spirit, indicating a temperature higher than before leaving, and it was closely approximate at all times to the temperature of the air. Consequently, notwithstanding the clearness of the sky, the loss of heat by radiation must have been small. No ozone was shown at the Royal Observatory, but in the balloon paper tests were coloured to 4, on a scale of greatest intensity being considered 10.

At the early part of this ascent I was wholly occupied with the instruments, and when at the height of about 1000 feet, the view which suddenly opened far exceeds description. Almost immediately under, but a little to the southeast, was Woolwich; north was Blackwall; south, Greenwich and Deptford; and west, as far as the eye could reach, was London-the whole forming a starry spectacle of such brilliancy as far to exceed anything I ever saw. When I have been at this elevation in the evening, at a distance from London, it has had the appearance of a vast conflagration, but on this night the air was so clear and free from haze that each and every light was distinct, and apparently all but touching each other.

The whole of Woolwich, Blackwall, Deptford, and Greenwich could be traced as a perfect model by the line of lights of their streets and squares. In nine minutes we were opposite Brunswick Pier, Blackwall, crossing the Thames, then passed across the Isle of Dogs, Greenwich Reach, and so up the River Thames. As we advanced towards London, the mass of illumination increased in intensity. At 6h 42m the South-Eastern Railway Terminus at London Bridge was directly under us; looking southward at this time we saw the Borough stretching far away, and the many streets shooting from it, particularly Southwark Street, with its graceful curve of lamps. In one minute more we were over Southwark Bridge, 1300 feet high, passed Blackfriars Bridge at 6h 45m, and Charing Cross at 6h 47m.

On leaving Charing Cross I looked back over London, the model of which could be seen and traced-its squares by their lights, the river, which looked dark and dull, by the double row of curved lights on every bridge spanning it. Looking round, two of the illuminated dials of Westminster clock were like two dull moons. Again, looking eastward, the whole lines of Commercial and Whitechapel Roads, with their continuations through Holborn to Oxford Street, were visible, and most brilliant and remarkable. We were at such a distance from Commercial Road that it appeared like a line of brilliant fire, assuming a more imposing appearance when the line separated into two, and most imposing just under in Oxford Street. Here the two thickly studded rows of brilliant lights were seen on either side of the street, with a narrow dark space between, but which dark space was bounded, as it were, on both sides by a bright fringe like frosted silver. At first I could not account for this appearance; but presently, at one point more brilliant than the rest, persons were seen passing, their shadows being thrown on the pavement, and at once it was evident this rich effect was caused by the bright illumination of the shop lights on the pavements.

I feel it impossible to convey any adequate idea of the brilliant effect of London, viewed at an elevation of 1300 feet, on a clear night, when the air is free from mist.

1866.

2 B