when they were burnt black opened the electrometer negatively. 56.-Hemp seed thrown upon the hot iron caused a weak positive repulsion, but when water was added it became strongly positive.

57.-A tea spoonful of water was dropped into the concave hot iron which did not produce any repulsion, then some powdered gum arabic was added, which caused the gold leaf to diverge positively, then bees wax was also added, which caused it to become negative. 58.-These two last substances were dropped on the hot iron in the reversed order, which first produced negative and then positive. 59.-Mustard seed was dropped upon the hot iron, which caused no repulsion till water was added to the burnt residuum, which opened the gold leaf negatively.

60.-Linseed produced no electricity till water was added to the black residuum, which opened the electrometer weakly negative. The iron was then made hotter, and the addition of water produced positive.

61.-Canary seed also produced negative by the addition of water till it was burnt very black, and then it became positive; also anise seed, and fennel seed, were like the canary.

62.-Burnt millet seed produced positive electricity with the addition of water.

63.-Water added to burnt coriander and cummin seeds produced negative electricity till the residuum had continued burning a long time, and then it became positive.

64.-Hitherto the electricity of the apparatus whence the vapours ascend has been only examined. I now fastened a piece of paper upon a bent wire, which being placed in the cap of the electrometer hung over the hot iron, so that the vapours in ascending might pass over the paper, and shew whether this electrical state would in any instance be of the same kind observed in the vessel.

65.-The vapour of red port wine was tried as above, and found positive, contrary to the state of the iron in exp. 29.

66.-The vapour of raspberry wine was found to be negative contrary to the state of the iron in exp. 30. Also wine made from bilberries, and sugar and water mixed, produced negative vapours.

67.-The vapour of pure water was positive, but the addition of a small quantity of saliva changed it to negative.

68.-The vapour of raisin wine was first positive and then negative, and the reverse when the iron was examined.

69.-As carraway seed produced negative electricity without the addition of water, and therefore without any visible vapour, except a little smoke, the paper fixed upon the electrometer was several times placed at different distances above the hot iron, whilst the carraway seeds were burning, but no electricity appeared.

70.-The square brick which supported the hot iron was placed in the middle of an earthen plate full of water, and standing upon the electrometer, then the hot iron being laid upon the brick and out of the reach of the water, wool was burnt upon it, and a spoonful of water added; lastly, the whole was covered with a glass jar

with its mouth immersed in the water, that the vapour might not escape without touching the water; in this experiment no electricity appeared.

From these experiments it appears that various mineral, vegetable, and animal substances when evaporated, cause a positive or negative divergency of the electrometer, and it was remarked, in the beginning of this section, that M. de Saussure attributed these effects to the generation of a new quantity of the electrical fluid; but since the state of the electricity of the ascending vapour is contrary to that of the insulated vessel whence it rises, it now seems more probable that the vapour thus produced acquires its positive or negative state because its affinity with the electrical fluid is greater or less than that of the vessel, and that when a particle of vapour is but just in contact with the surface whence it rises, its capacity to become positive or negative is much greater than when it is entirely surrounded with air; and thus if the vapour becomes positive by absorbing electricity from the vessel, the vessel will become negative, and v. v., without the necessity of supposing a new quantity of the fluid to be generated in this process.

The above extensive experiments of Mr. Bennet, which were, no doubt, made with great care, are not attended with those uniform results as might have been expected, from the views we have hitherto taken on this subject; and it is probable that those aberrations which are so conspicuous in several cases, might be traced to some other cause than that of simple evaporation; but as we have not yet repeated these experiments, any further remarks on them, in this place, would certainly be premature.

EXPERIMENTS BY DR. CHARLES SCHAFHAENTL.

The experiments of this gentleman were made in the Royal Adelaide Gallery, and in consequence of his considering that the electric phenomena of steam boilers being dependent on the incrustations which they contain, he selected one of Marcet's common boilers, in preference to one of Mr. Perkins's kind, in which incrustation is prevented. The boiler selected was globular, of iron, and about five inches diameter. In the vertical axis of this experimental boiler was a mercurial guage, and at the distance of about 45° from it, downwards, was a thermometer; and on the opposite side of the globe, a jet with a stopcock. The lower part of the cavity of the boiler was occupied by the mercury belonging to the steam guage, and on the top of this mercury an inch and a quarter deep of distilled water was placed. A glass bell, nine inches diameter, and five inches deep, was suspended with its axis in the axis of the jet continued, having the muzzle in the direction of the jet, at about four inches distance. The greater portion of a bundle of copper wire was inserted in the bell, and the remote end of the wire was connected with a gold leaf electroscope, furnished with a condenser. When the water in the globe had boiled to a sufficient extent to raise the mercurial gage to thirty-one inches, the stopcock of the jet was

opened, and the issuing steam condensed in the bell, and in a few seconds the gold leaves diverged to a great extent, with positive electric action, even without removing the insulated plate of the condenser. But when the steam was directed to the wire only, outside of the bell, no electric action was observable, for the very obvious reason that the condensation of steam was too trifling to show it.

When the water last used was drawn off, and replaced by a saturated solution of common salt, and afterwards boiled as in the previous case, no trace of electric action could be discovered. After this fact was ascertained, the boiler was cleansed of its saline contents, and filled with distilled water, which was boiled till the steam again arrived at a pressure of thirty-one inches of mercury; but in this case the electroscope could not be affected. When, however, the water was reduced to about the same quantity as at first, the condensed steam gave electrical indications. Several other variations of the experiments were made with various results, though in all cases where electrical indications were afforded, they were of the positive action. Dr. Schafhaentl was, however, led to suppose that the success of the experiments depended entirely upon that state of the escaping steam which caused a peculiar fluttering noise, which happened only when the boiler was charged with about an inch and a half deep of water; for when the steam ceased to make that fluttering noise, although at a pressure of thirty-two inches of mercury, would even cause the previously diverged gold leaves to speedily collapse.

This peculiar noise, which appeared to be so essential to the production of electricity by steam, Dr. S. supposes to be owing to the sudden boiling of the water, and the conversion of a portion of it into a fine spray; under which circumstances the issuing steam deposited a large quantity of water in the bell glass, which often ran in streams from its lower edge. Insulation of the boiler did not appear to affect the results of the experiments, the electrical action being to the same amount whether the apparatus was insulated or not. "A proof," says Dr. S., "that the electricity of the steam developed in the glass bell could not be contained in the steam during its passage through the three-inch long metallic jet of the boiler, as all the electricity would have been deposited in this narrow metallic passage." Dr. S. is led to suppose that a partial condensation of the steam into mist, for instance, is not sufficient to produce electric action, as its conversion into water appeared to be requisite for electrical developement. From this circumstance the Doctor supposes that he has discovered some clue to direct him to the cause why certain clouds only, are capable of producing thunder storms. He says that " a common cloud, consisting only of moisture, seems to be analogous to a pure jet of steam in the glass bell, both consisting of minute hollow water globules, or bubbles, leaving only a small deposit of moisture in the glass bell, or in the air, which finally collects into small drops of rain. But when the steam depo

• Of course Dr. S. meant that it was not sensible in that tube.

sits rapidly a great quantity of liquid water, which in a thunder cloud produces those well known heavy showers, electricity is set free in great quantities, so that a jet of issuing steam from Marcet's boiler, in three seconds produced the same effect on the gold leaves of the electroscope as a feeble spark from an electric machine, with a glass plate of nine inches diameter, produced in damp weather."

The general tenor of these speculations in the analogy, appears to be perfectly correct; at least it is in accordance with our own views on the subject; but we are very far from entertaining the opinion that the steam, whilst passing through "the three-inch long metallic jet," was not electrical. For such an opinion, if correct, would at once extinguish the idea, "that a partial condensation of the steam into mist, is not sufficient to produce electric action." For if the law of electric developement holds good in one stage of condensation, it must also hold good in every other stage. And, although the misty steam produced no sensible electric action in the experiments in question, that was no reason for supposing that no such action was present in the steam within the jet; but on the contrary, it would lead us to infer that the steam within the jet pipe was electro-negative, and its conversion into mist within the bell, brought it to its natural electric state of neutrality: and that a further condensation lessened its electric capacity another stage, by which means it became electro-positive, as shown by the experiments. These are the theoretical views we have always entertained on this interesting subject, whether the steam be produced and recondensed artificially, or by the usual processes of nature; and hence it is that we cannot entertain the idea of any dense cloud being in a negative electric state, unless influenced by the repulsive electric action of some other vicinal cloud more densely electrical than itself.

An experimenter would easily discover that Dr. S.'s electroscope was not of the most delicate kind, or its indications would not have been compared to those produced by a "spark;" for it is well known that a spark, however feeble, would immediately spoil a delicate gold leaf electroscope.

Although by some of the experiments already described, Dr. S. could not detect electric action when the boiler was charged with salt water, it is stated by that gentleman, that, in subsequent experiments, "if the water in the boiler was saturated with common salt, or with sulphate of lime, and even a slight excess of sulphuric acid, the angle between the diverging gold leaves remains the same as if distilled water was used." Hence, he very justly infers, "6 that the observed free positive electricity, in this case, was solely attributable to the sudden condensation and separation of water from steam, &c." And he might as justly have stated, that all electro-positive actions from steam or the vapour of water, depend on condensation. Hence, generally, whether the vapours be produced slowly or rapidly, it is first electro-negative, next, by a certain degree of condensation, electro-neutral, and, finally, electro-positive by every future degree of condensation.-EDIT.

ON VOLTAIC PILES.

Having so many solicitations from various quarters for information on several points in the history of electricity, and also respecting certain pieces of apparatus, especially in voltaic electricity, it would be difficult to know where to begin to give satisfaction to all parties. However, as some of our correspondents are anxious to know how to construct the dry electric pile, and others wish to have information respecting the earliest experiments in galvanism, we shall endeavour to satisfy both inquiries on these connected subjects, by giving the best data that we can procure from the accounts given by the authors themselves of their respective discoveries.

It appears that in the year 1767, a work, entitled "The General Theory of Pleasures," was published by M. Sultzer, in which the author describes the following experiment:- "Take two pieces of metal, one of silver, the other of lead, and bring their edges into contact with each other; and while thus connected, place them both on the tongue : a taste will be experienced similar to that produced by vitriol of iron (sulphate of iron). But no trace of any such taste is perceived by the application of either metal individually." Sultzer does not say whether he placed on the tongue each metal separately whilst in contact with the other, or whilst entirely alone; but it may possibly be useful to some readers to know, that the experimenter will find no difference in the effect, whether the metal placed on the tongue be in contact with another metal or not, provided this latter metal be not also in contact with the tongue, or some other moist part of the body. Under the latter circumstance, however, even by holding the second metal with the finger and thumb, if perspiring, or otherwise moistened, the peculiar taste will be felt. Although the experiment of Sultzer is of that class which has received the title galvanic," it was not till about twenty-four years afterwards, viz., 1791, that Professor Galvani made his discovery, which led to this branch of electricity. The following account of this discovery, given by M. Volta in two letters to Cavallo, will always be found interesting.

The subject of these letters, says M. Volta, is that of animal electricity, discovered by Dr. Galvani, and publised by him in a work entitled, "Aloysii Galvani de Viribus Electricitatis in Motu Musculari Commentarius. Bononiæ, 1791." This subject, under the name of galvanism, has given occasion to several important discoveries, having been very much cultivated by many respectable philosophers, and by none more than by those of England.

Dr. Galvani having cut and prepared a frog, so that the legs hung on one side of the spine of the back, separate from the rest of the body, solely by the crural nerves laid bare, he found that there were produced very quick motions ni the legs, with spasmodic contractions in all the muscles, whenever a spark was taken from the prime-conductor of an electric machine, not on the body of the