of an electro-negative body, were it not for the numerous exceptions which exist to the rule, some very remarkable instances of which I shall have occasion to notice in the sequel. Hence it is always necessary, in order to discover those exceptions, and to verify the weight of the volume sought to compare the result of the preceding calculation with the known degrees of oxidation of the substance whose volume is wanted. If, for example, we find that an acid or electro-negative oxide is neutralized by a quantity of base or electro-positive oxide which contains of the oxygen in the acid, this acid will appear to contain 3 volumes of oxygen. But if among the oxides of the radicle of this acid we find one which contains half the oxygen of the acid, it is clear that the saline combination in question is an exception, and that the acid must contain 6 instead of 3 volumes of oxygen. I refer, for a farther explanation of this, to what I shall say in the sequel concerning arsenic and chromium.

The preceding observations explain why, when a salifiable base has combined with more oxygen, it requires always an additional volume of acid for every volume of oxygen which it has absorbed. It is for the same reason that oxygen appears to determine exclusively the composition of bodies; though there can be no doubt that every element contributes equally to that composition.

While treating in the sequel of each particular substance, I shall explain the way in which I determine the weight of a volume of it, and likewise state the experiments on which the calculation is founded. As none of our experiments, except from accident, can be perfectly correct, and as a small error in the result often increases in the calculation, it is not possible that my determinations can be perfectly exact: but I hope to approach within very near limits, at least, of the truth. The difference in the analytical results will point out to us the limits of error, and show us degrees beyond which our determinations cannot be incorrect. I shall give an account of these minima and maxima indicated by experiment, as well as of the experiments themselves, which point them out. We have, for example, every reason to believe that a volume of sulphur weighs 201 but some experiments raise it as high as 210, while others sink it as low as 200. As we cannot determine at present which of these numbers is most exact, it is good to know within what limits our knowledge is uncertain.

ta

As far as I know, the English chemists Dalton, Davy, and Young, are the only persons who have yet attempted to make these determinations; and they have proceeded in a manner somewhat different. Mr. Dalton, to whom the honour of the first attempt is due, has endeavoured to determine the relative

weights both of simple and compound atoms. (New System of Chemical Philosophy.) Davy, though he has not adopted the atomic theory of Dalton, has embraced the doctrine of definite proportions; and what Dalton calls an atom, he calls a proportion. (Elements of Chemical Philosophy.) Dr. Young, in his Introduction to Medical Literature, has made similar determinations; but what Davy calls proportion, Young calls combining weight. But none of these philosophers have attempted to give any great degree of exactness to their determinations. They have frequently even omitted stating the experiments from which these determinations are derived. The method which they have adopted of giving round numbers, though it facilitates the recollection and calculation, is scarcely consistent with the object of scientific researches, and ought to be rejected for even supposing that perfect exactness could never be obtained, it is nevertheless the object towards which all our efforts should be directed.

(To be continued.)

ARTICLE VIII.

Magnetical Observations at Hackney Wick. By Col. Beaufoy. Magnetical Observations.

Latitude 51° 32′ 40′′ North. Longitude West in Time 6"

Oct. 20.-The needle at noon vibrated at times six minutes the next day the wind blew from the S. Es with rain.

Nov. 11. The variation extraordinary this morning, in the evening there was a violent storm from the S.W. which lasted 36 hours, and the gusts were remarkable for their strength and frequency.

Nov. 15. At noon the needle was steady, until it began to rain; it then vibrated five minutes and ten seconds.

༣་

Nov. 17-At the commencement of the snow storm the needle vibrated eight minutes and thirty seconds.

ARTICLE IX.

Account of a luminous Meteor seen at Sunderland. By Mr.

SIR,

Renney.

(To Dr. Thomson.)

Bishopwearmouth, Nov. 12, 1813.

PERMIT me, through the medium of your Journal, to lay before your readers the following particulars of what I consider a very uncommon phenomenon; in the hope that you, or some other scientific Gentleman, will have the goodness to afford an explanation through the same channel.

On Wednesday evening, the 10th of this month, about 40 minutes after six, the moon having just risen, but was not visible, owing to a very dense cloud (whose altitude was 7°), the most opaque ever recollect to have seen. From behind this cloud there appeared a stream of light, which extended across the hemisphere, and so dense that y in Pegasus, and a in Aquila, were obscured by it; the edges of which at intervals diverged into lines, diminishing its breadth: but, that I may afford a more perfect idea, I shall give its extent by the stars that appeared in or near the northern and southern edges:

On the Northern Edge.

α

It was obscured by a dark cloud in Taurus Poniatowski, and extended visible through Serpentarius to the horizon.

"

I immediately waited upon Thomas Jones, Esq. a Gentleman of considerable scientific acquirements, who possesses a very excellent astronomical and philosophical apparatus (to whom I am under many obligations for their use); and although he was at home, and disengaged, I found that before he could come to the door this immense volume of light had lost much of its lustre, and was so reduced in substance that in Pegasus now became visible near the centre. Mr. Jones observed, that he "had seen many uncommon phenomena of nature, but none like the present." Its duration, I believe, did not exceed six minutes; for, at the time I first saw it, I think it was then in its

greatest splendour, but in about three minutes it entirely disappeared.

In the north the Aurora Borealis was faintly playing, from which to the south the heavens (except the cloud before alluded and a cloudy horizon) were clear, and had the appearance of frosty weather. The wind at the time was easterly, and much rain had fallen during the day..

:

I am of opinion that this phenomenon could not be caused by the above-mentioned cloud concentrating the rays of the rising moon; for if it had, it could not have caused it either to extend across the whole hemisphere, nor to have had that density which this possessed and at the same time I may remark, that the moon was not the centre; but, on referring to a celestial globe, will be found to have been to the north of it; consequently, if the moon had caused this luminous appearance, it would have been in a different direction; besides, the stream of light was not in a right line, but rather bearded to the north.

I am, with much respect, Sir,

Your most obedient humble servant,

ROBERT RENNEY.

ARTICLE X.

ANALYSES OF BOOKS.

A

A short Account of Experiments and Instruments depending on the Relation of Air to Heat and Moisture, Svo. By John Leslie, F.R.S.E. Professor of Mathematics in the University of Edinburgh.

Mr. Leslie has already gained considerable reputation by his curious experiments on the effect of surface on the rate of cooling or heating, which he published about nine years ago. In the present little tract he gives us his opinions respecting the nature and effects of heat in general and makes us acquainted with some important facts which he has ascertained respecting evaporation, the dryness and moisture of air, and the mode of producing cold by evaporation. He describes a variety of instru-ments which he has contrived for this kind of investigation. The book is written with considerable perspicuity; and, as far as I can judge, the style is greatly preferable to that of Mr. Leslie's other literary productions. No great attention has been paid to accuracy of arrangement; and Mr. Leslie introduces without ceremony (as has always been his habit) any topic which strikes his fancy, whether it bears upon the subject in hand or not. Perhaps the subjects treated of in this work are of so unconnected

V