charged, the spark passed through nearly as much space as in common air, and with a light visible in the shade. At all temperatures below 200", the mercurial vacuum was a much worse conductor than highly rarefied air: and when the tube containing it was included in the exhausted receiver, its temperature being about 50°, the spark passed through a distance six times greater in the Boylean than in the mercurial

vacuum.

It is evident from these general results that the light (and probably the heat) generated in electrical discharges depends principally on some properties or substances belonging to the ponderable matter through which it passes; but they prove likewise that space, where there is no appreciable quantity of this matter, is capable of exhibiting electrical phænomena; and, under this point of view, they are favourable to the idea of the phænomena of electricity being produced by a highly subtile fluid or fluids, of which the particles are repulsive, with respect to each other, and attractive of the particles of other matter. On such an abstruse question, however, there can be no demonstrative evidence. It may be assumed, as in the hypothesis of Hooke, Huygens, and Euler, that an ethereal matter, susceptible of electrical affections, fills all space; or that the positive and negative electrical states may increase the force of vapour from the substances in which they exist; and there is a fact in favour of this last idea which I have often witnessed-when the Voltaic discharge is made in the Boylean vacuum, either from platinum or charcoal, in contact with mercury, the discharging surfaces require to be brought very near in the first instance; but the electricity may be afterwards made to pass to considerable distances through the vapour generated from the mercury or charcoal by its agency; and when two surfaces of highly fixed metal, such as platinum or iron, are used, the discharge will pass only through a very small distance, and cannot be permanently kept up.

The circumstance, that the intensity of the electrical light in the mercurial vacuum diminishes as it is cooled to a certain point, when the vapour must be of almost infinitely small density, and is then stationary, seems strongly opposed to the idea, that it is owing to any permanent vapour emitted constantly by the mercury. The results with tin must be regarded as more equivocal; because as this substance cannot be boiled. in vacuo, it may be always suspected to have emitted a small quantity of the rare air or gas to which it has been exposed: yet, supposing this circumstance, such gas must be at least as highly expanded as the vapour from cooled mercury, and can hardly be supposed capable of affording the dense light, which

the

the passage of the electricity of the charged Leyden phial through the vacuum produces.

When the intense heat produced by electricity is considered, and the strong attractive powers of differently electrified surfaces, and the rapidity of the changes of state, it does not seem at all improbable, that the superficial particles of bodies, which, when detached by the repulsive power of heat, form vapour, may be likewise detached by electrical powers, and that they may produce luminous appearances in a vacuum, free from all other matter by the annihilation of their opposite electrical

states.

In common cases of electrical action, the quantity of the heat generated by the annihilation of the different electrical states depends, as I stated in my last communication to the Society, upon the nature of the matter on which it acts; and in cases when electrical sparks are taken in fluids, vapour or gas is always generated; and in elastic fluids, the intensity of the light is always greater, the denser the medium. The luminous appearances therefore, it is evident from all the statements, must be considered as secondary; whilst the uniform exertions of electrical attractions and repulsions, under all circumstances, in rare and dense media and in vacuo, and with respect to solids, fluids, and gases, point them out (whether they be specific affections of a subtile imponderable fluid, or peculiar properties of matter) as primary and invariable electrical phæno

mena.

I have mentioned in the last page the suspicion, that melted tin may contain air. I shall conclude this paper by stating the grounds of this suspicion, and noticing a circumstance which appears to be of considerable importance, both in relation to the construction of barometers and thermometers, and to the analysis of gaseous bodies. Recently distilled mercury that has been afterwards boiled and cooled in the atmosphere, and which presents a perfectly smooth surface in a barometer tube, emits air when strongly heated in vacuo, and that in quantities sufficient to cover the whole interior of the tube with globules; and on keeping the stop-cock of one of the tubes used in the experiments on the mercurial vacuum open for some hours, it was found that the lower stratum of mercury had imbibed air, for when heated in vacuo, it emitted it distinctly from a space of a quarter of an inch of the column: smaller quantities were disengaged from the next part of the column; and its production ceased at about an inch high in the tube. There is great reason to believe, that this air exists in mercury in the same invisible state as in water, that is, distributed through its pores; and the fact shows the necessity of long boiling the Vol. 60. No. 293. Sept. 1822. mercury

A a

mercury in barometer and thermometer tubes, and the propriety of exposing as small a surface of the mercury as possible to the air. It may explain, likewise, the difference of the heights of the mercury in different barometers; and seems to indicate the propriety of reboiling the mercury in these instruments after a certain lapse of time.

Explanation of the Figure.

A. The tube, of the usual diameter.

B. The wire for communicating electricity.

E. A small cylinder of metallic foil, to place as a cap on tubes not having the wire b, to make a coated surface.

c. The surface of the quicksilver, or fused tin.

D. The part of the tube to be exhausted by the stop-cock F, after being filled by means of the same stop-cock, when necessary, with hydrogen.

G. The moveable tube connected with the air-pump.

It is evident, that by introducing more mercury, the leg d may be filled with mercury, and the stop-cock closed upon it, so as to leave only a torricellian vacuum in the tube, in which the mercury may be boiled. I have found that the experiment tried in this way, offers no difference of result.

XXXI. On Mr. JOHN MOORE Junior's "Reply."

To the Editors of the Philosophical Magazine and Journal. GENTLEMEN, -I

REPEAT that I see no necessity whatever for republishing on the part of Mr. John Moore junior that which I had already done. The public have nothing to do with private intromissions. It was priority of publication which secured for Sir H. Davy the imperishable honours attached to his beautiful invention. It is this which is the standard of appeal in science and art.

I have given my reasons for rejecting the cumbrous and troublesome modification obtruded. These reasons remain inviolate.

The "Reply" is a mere tissue of questions: FOURTEEN marks of interrogation are interspersed! A very convenient mode of "reply," it must needs be confessed. For instance, I am asked, "How is it that the individual becomes reanimated?" This is introduced as a species of climax to a most disingenuous (I shall not term it wilful or malignant) perversion of my language. Mr. Moore junior says," Mr. Murray has stated that the air undergoes no change whatever!!" Whereas my words are," the air undergoes no change whatever until natural respiration returns.” There

There is not a word more that calls for notice; the remainder of these interrogatories being awkwardly apologetic, rather than any thing else.

I have the honour to be, gentlemen, Your much obliged and very obedient humble servant, August 2, 1822. J. MURRAY.

XXXII. On the Cause of a singular partial Failure in a Crop of Turnips. By Mr. SAMUEL TAYLOR, of Bungay. To the Editors of the Philosophical Magazine and Journal. GENTLEMEN, -As I find you do not exclude from your pages any information, however humble, on subjects connected with the study and practice of agriculture, allow me to lay before you a singular instance of partial failure in a field of turnips, which has recently come under my observation. This field is in the hands of my friend and neighbour Mr. Stamford, of Ditchingham, near this place. It may be necessary here to remark, that it is usual, in working our fallows intended for turnips, to cross-plough the land twice, in order to get the field perfectly level previous to stetching or ridging it up for the ensuing crop. Now the ridges or stetches of this field run north and south; but the failure in the turnip crop above mentioned extends across, not lengthways of the ridges, and consequently in the direction of the warting.

The following sketch may give a clearer idea than mere description can convey of my meaning, and of the present appearance of the field.

N

b

May: good healthy plants.

с

d

Left unploughed from mid

d

dle of May to beginning

of June: a total failure

d

of plant.

Now what has occasioned this failure? and on what principle can we account for the narrow strips of good healthy plants A a 2

across

across the field at a and b, whilst those on each side of them have totally failed? An inquiry into the mode of culture will, perhaps, explain what at first sight appears rather mysterious. It seems that the field was warted or cross-ploughed for the first time about the middle of April; the wheat stubble having been first turned in, as we call it, i.e. ploughed, before winter. It was again warted the beginning of May. The whole field was stetched up for sowing about the beginning of June (being the fourth earth it had received); but in consequence of the long drought, it was not sown till the 12th of July. The seed (Swedish) was put on broadcast in one day. The plants came to the hoe in about a month after; but for some time previous to hoeing, a partial deficiency of plant was noticed. Mr. S. was for a while at a loss to account for so singular and regular a failure, until reminded by his men of a circumstance which had escaped his recollection. The part of the field No. 1 lies lower, and is consequently more liable to injury from wet, than the upper part, No. 2. Having therefore finished crossploughing No. 1, he, knowing from the dryness of the soil that No. 2 could be ploughed at any time, took off his men and horses to some other work of more immediate importance; so that the whole of No. 2, except a few furrows which had been ploughed (marked a and b), lay for above a fortnight untilled. The deficiency of plant is therefore clearly attributable to this circumstance, because the whole of the remainder of the field, including the strips a and b, produced good healthy plants: but then occurs the question, How could this suspension of operations for two or three weeks occasion such extraordinary effects? The answer appears to be this: The ground not being stirred during this interval, a multitude of grubs and wireworms were thereby suffered to hatch, which the plough would otherwise have destroyed; and these have doubtless eaten the plants. This idea appears to derive confirmation from the number of rooks which have ever since continued to alight on the bare spots: on removing the surface earth of which, both grubs and wireworms are still found just

buried beneath the mould.

Perhaps some of your readers better versed in these matters than I am, can give a more satisfactory solution of the above phænomenon. I merely state the facts, and endeavour to put the most reasonable interpretation on them in my power. If I am right, it would follow that it is not good to allow too long an interval between the spring ploughings; but I should be glad to know the opinion of entomologists on this subject. In the mean time, I remain, gentlemen,

Your most obedient humble servant, Bungay, Suffolk, Aug. 20, 1822. SAMUEL TAYLOR.