The number of experiments made up to the height of 7,000 feet varying from 21 to 60 in each 1,000 feet as taken in the last three years, are sufficient to enable us to speak with confidence; the results are, that the temperatures of the dew point as found by the use of the dry- and wet-bulb thermometers, and my hygrometrical tables, are worthy of full confidence up to this point. At heights exceeding 7,000 feet, the three years' experiences do not yield a sufficient number of experiments to give satisfactory results. Before we can speak with certainty at these elevations more experiments must be made.

Let us take the balloon as we find it, and apply it to the uses of vertical ascent; let us make it subservient to the purposes of war, an instrument of legitimate strategy; or employ it to ascend to the verge of our lower atmosphere; and as it is, the balloon will claim its place among the most important of human inventions, even if it remain an isolated power, and should never become engrafted as the ruling principle of the mechanism we have yet to seek.

Whether we regard the atmosphere as the great laboratory of changes which contain the germ of future discoveries, as they unfold to the chemist, the meteorologist, the physician; its physical relation to animal life at different heights; the form of death, which at certain elevations is certain to take place; the effect of diminished pressure upon individuals similarly placed; the comparison of mountain ascents with the experiences of aëronauts; these are some of the inquiries which suggest themselves, and faintly indicate researches which naturally ally themselves to the course of balloon experiments.

Sufficiently varied and important they will be seen to rank the balloon as a valuable aid to the uses of philosophy, and rescue it from the impending degradation as a toy, fit only to be exhibited or to administer to the pleasures of the curious.

Already it has done for us that which no other power has accomplished; it has gratified the desire natural to man, to view the earth in a new aspect, and to sustain himself in a new element, hitherto the exclusive privilege of birds and insects. We have been enabled by its aid to ascend among the phenomena of the heavens, and to exchange conjecture for instrumental facts, recorded at twice the elevation the highest mountain permits us to observe.

[J. G.]

GENERAL MONTHLY MEETING,

Monday, April 3, 1865.

WILLIAM POLE, Esq. M.A. F.R.S. Treasurer and Vice-President, in the Chair.

Walter Armstrong, Esq.

Robert Birkbeck, Esq.

Henry Brandreth, Esq. M.A.

James William Butler, Esq.

The Rev. Tullie Cornthwaite, M.A. F.L.S.

George Duppa, Esq.

Mrs. Margaret Henry.

Henry Mather Jackson, Esq.

Major William Lyon.

Sir Theophilus Metcalfe, Bart.
Alexander McDonald, Esq.
Colonel Robert Morrieson.

were elected Members of the Royal Institution,

John James Unwin Clarke, jun. Esq.
Richard Belgrave Jackson, Esq.

John Macpherson, Esq.

were admitted Members of the Royal Institution.

The Managers reported, That, in pursuance of the Actonian Trust Deed, they had awarded one prize of One hundred guineas to an essay on "The Phenomena of Radiation, as exemplifying the Wisdom and Beneficence of God," by George Warington, F.C.S. The other hundred guineas (not awarded in 1858) were ordered to be reserved to the next award of the Actonian prize, none of the other Essays being, in the judgment of the Committee of Managers, of sufficient merit to entitle the author thereof to such prize.

The PRESENTS received since the last Meeting were laid on the table, and the thanks of the Members returned for the same: viz.— FROM Agricultural Society of England, Royal-Journal. Second Series. Vol. I. Part 1.

8vo. 1865.

Astronomical Society, Royal-Monthly Notices, 1864-5. No. 4. 8vo.
Basil Natural History Society-Verhandlungen. IV. 1. 8vo.

1864.

British Architects, Royal Institute of-Sessional Papers. 1864-5. II. 4. 4to. Cator, C. O. F. Esq. M.A. M.R.I. (the Author)-Meteorological Diagram for

Pharmaceutical Journal for March, 1865.

Practical Mechanics' Journal for March, 1865.

4to.

Geographical Society, Royal-Proceedings. Vol. IX. No. 2. 8vo. 1865.

Hawkins, Charles, Esq. F.R.C.S.E. (the Editor)-The Works of Sir B. C. Brodie.

3 vols. 8vo. 1865.

Horticultural Society, Royal -Proceedings, 1865. No. 3. 8vo.

Linnean Society of London-Transactions. Vol. XXIV. Part 3.

4to. 1864.

Mechanical Engineers' Institution, Birmingham-Proceedings, August, 1864.

Part 1. 8vo.

Meteorological Society, British-Proceedings, No. 17. 8vo. 1865.

Moore, Charles H. Esq. M.R.I.-New Entozoötic Malady. By T. S. Cobbold, M.D. (K 91) 8vo. 1865.

Petermann, A. Esq. (the Editor)-Mittheilungen auf der Gesammtgebiete der Geographie. 1865. No. 1. Ergänzungsheft, 15. 4to.

Photographic Society-Journal, No. 155. 8vo. 1865.

Pritchard, The Rev. Charles, F.R.S. (the Author)-Eloge of Struve. (From Proceedings R. Ast. Soc. 1864.)

Treasurer of St. Bartholomew's Hospital, London-Statistical Tables of the Patients in the Hospital in 1864. 4to.

Vereins zur Beförderung des Gewerbfleisses in Preussen-Verhandlungen, November und December, 1864. 4to.

Wilkins, W. Noy, Esq. (the Author)—Art Impressions of Dresden, Berlin, and Antwerp. 16to. 1860.

Royal Institution of Great Britain.

WEEKLY EVENING MEETING,

Friday, April 7, 1865.

H.R.H. THE PRINCE OF WALES, Vice-Patron, in the Chair.

DR. A. W. HOFMANN, F.R.S.

On the Combining Power of Atoms.

YOUR ROYAL HIGHNESS, LADIES AND GENTLEMEN,

You observe on the lecture-table a great number of bottles, containing an almost perplexing variety of chemical substances; the walls of the theatre are covered with diagrams exhibiting an endless number of formulæ, which some of my audience, I have no doubt, are contemplating with mixed feelings of uneasiness and resignation. Nor will it diminish your discomfort if I tell you that each of the substances on the table represents at least a thousand bodies actually known, and again that each of the known bodies represents a million or more bodies which are not known, but which exist well defined in the mind of the chemist who calls them into life whenever he requires them for purposes theoretical or practical. At the first glance, I admit this is rather a formidable array; but our anxiety is materially lessened, if we learn that this host of substances is formed according to simple laws which it is in our power to discover, and which by the united efforts of chemists are gradually unfolding themselves.

May I be permitted this evening to call your attention to some of the laws, or at all events law-like regularities, recently observed, and which are at present engrossing the interest of the leading chemists of all countries.

I would commence with one of the simplest of experiments :-Here are two gases, hydrogen and chlorine, the one a colourless inodorous gas, which burns quietly with a pale flame, the other a greenish yellow gas, possessing a suffocating odour, and not inflammable. When equal volumes of these two gases are mixed together, and a light applied to VOL. IV. (No. 42.)

2 G

the mixture, an explosion takes place, a compound gas being produced, which fumes in the air, and which, when dissolved in water, constitutes the spirit of salt, or muriatic acid of the earlier chemists, now called hydrochloric acid.

By certain processes, which we must not inquire into at the present time, the compound of hydrogen and chlorine, called hydrochloric acid, may be made to unite with another gas, oxygen; the combination giving rise to the formation of an acid called hypochlorous acid, and by which most of the bleaching operations carried out in commerce are effected. On plunging an appropriately-prepared piece of Turkeyred calico into a warm solution of chloride of lime, which is closely related to hypochlorous acid, you observe that a white pattern is produced on the cloth.

Again, an additional quantity of oxygen may be united to hypochlorous acid, when the compound called chlorous acid is formed. A well-known salt of commerce, chlorate of potassium, is generally used for its preparation. This salt is readily decomposed by acids. The explosive violence with which sulphuric acid acts upon it, the detonation attended by flashes of light, are phenomena early and frequently observed by the laboratory student. By substituting nitric for sulphuric acid, an explosive gas is formed, which, when dissolved in water, constitutes the chlorous acid in question.

A third compound, chloric acid, may be formed by the addition of a further dose of oxygen to chlorous acid. The most familiar salt of this acid is the chlorate of potassium just mentioned. This, as well as other derivatives of chloric acid, is largely used for pyrotechnic purposes. Here we must be satisfied with calling attention to a species of white gunpowder which has been lately devised, and which consists of a mixture of the potassium salt with tannic or gallic acid.

Lastly, by still further increasing the supply of oxygen, a fourth compound, perchloric acid, is produced. This substance again exhibits the explosive habitudes of the group of bodies in question. When made to combine with aniline, for instance, perchloric acid gives rise to a compound which goes off when heated in a test-tube, burning, as you observe, with an intense white light.

A glance at the diagram shows us the regularity with which the amount of oxygen increases in this series of oxygenetted derivatives of hydrochloric acid. There is nothing arbitrary in this accession ; each increment ensues step by step.