they were circles passing through the points in which these primary sets intersected each other. But I shall not attempt a particular description of the phenomena, because they could hardly be rendered intelligible without figures. V. ELECTRICITY. 1. A set of observations on the electricity of the atmosphere during thunder-storms, rain, and snow, has been published by Dr. Schubler, of Hofwyl. He has given four examples, which are rendered easily intelligible by the graphical representation in Plate XLII. The changes in the state of the electricity take place so suddenly that it requires some dexterity to observe them and note them down. In the plate the horizontal line represents the time from minute to minute; the perpendicular line denotes the degrees of the electrometer; the curve line within the scheme of course represents the position of the electrometer at the time specified in the horizontal line. The first scheme represents the variation of the electrometer during a thunder storm, which passed by at a distance. Warm weather had preceded April 11, 1806, on which the thunder storm took place; the day was cloudy, with a north-west wind, and a low barometer; the thermometer at two o'clock stood at 57°; the height of the place where the observations were made was 1705 English feet above the level of the sea; the electricity of the atmosphere during the day had been weakly positive; about six in the evening it began to rain, and the electricity of the rain was negative; at seven the rain stopped; but the sky was covered with gloomy clouds, and a thunder storm commenced towards the south-west, with distant thunder and lightning; the electricity of the air continued still negative; but at each flash of lightning its negative state was suddenly diminished, the hand of the electrometer approached 0, but returned almost immediately after the flash nearly to its original position, As the thunder storm approached nearer, the negative state of the atmosphere diminished. At 14 minutes past seven it became suddenly null, and even weakly positive, after a flash of lightning; but almost immediately after resumed its negative state. At 18 minutes after seven it became wholly positive; but the plate will show the changes which the electrometer underwent better than any description. The three remaining examples will be sufficiently understood from the figures. In the second of them the thunder was over head. 2. It is generally known that when a pointed metallic body is attached to the prime conductor of an electrical machine, the electricity does not accumulate in the conductor, but makes its escape from the extremity of the pointed body in a visible stream of light. Professor Hildebrandt has lately made a comparative set of experiments in order to determine which metal, when placed in these circumstances, sends off the greatest visible stream of light. The metals were all made into cones with blunt summits, and they were put upon the top of a brass rod attached to the upper part of the prime conductor. The following is the order which the metals tried followed, beginning with the one which emitted the greatest quantity of light, and terminating with that metal which gave out the least light: Antimony. Gold. Nickel. Silver. Brass. ·- 3. It is well known that the phenomena of galvanism have been accounted for by three different hypotheses, and that philosophers are not yet agreed which of these is the true one. According to the first opinion, which is Volta's, the phenomena are purely electrical, and depend upon the different states of electricity in the two metals employed. The chemical phenomena are merely accidental consequences of the electric discharge. According to another opinion, which is that of Berzelius, the phenomena are purely chemical, and the electricity is merely set at liberty in consequence of the chemical actions. A third hypothesis, that of Davy, unites the two preceding ones together, and considers the phenomena as partly electrical and partly chemical. Professor Pfaff, of Kiel, has published an elaborate examination of these three hypotheses. He endeavours to refute the hypothesis of Berzelius, and to establish that of Volta. I cannot pretend to give an abstract of this memoir here; because it could scarcely be rendered intelligible without a pretty full enumeration of the galvanic phenomena and experiments; an enumeration which would take up much more room than I can possibly spare. But the memoir is well worthy of the attention of all those persons who are interested in electricity or galvanism. I know of no treatise in which a greater quantity of information on the subject is given in less space. (See Schweigger's Journal, x. 179.) 4. De Luc's curious discovery of a dry galvanic pile which continues active for years with little interruption, and likewise his explanation of the voltaic column founded on that discovéry, and on his previously published theory of electricity, are known, I presume, to most of my readers, as they were published about five years ago in Nicholson's Journal, and have attracted the general attention of electricians. Zamboni, Professor of Natural Philosophy in the Lyceum at Verona, has made an alteration in the construction of De Luc's pile. He presented one of his electromotors, as they have been called, to the Royal Society, and they may be seen commonly enough in the mathematical instrument-makers in London. His pile consists of slips of silver paper laid on each other. On the unsilvered side of the paper is put a layer of black oxide of manganese and honey. These papers are piled above each other to the number of 2000. They are then covered externally with a coating of shell lac, and inclosed in a hollow brass cylinder. Two of these piles are placed at the distance of four or five inches from each other; and between them is suspended a light metallic needle on a pivot, which is attracted alternately to the one pile and the other, so that it constantly moves between them like a pendulum. Attempts have been made to make this electric pendulum the moving power of a clock or watch; and these attempts have to a certain degree succeeded. Dr. Iäger, of Stuttgardt, has made a number of experiments upon this pile, both as modified by De Luc and by Zamboni. But on looking them over in a cursory manner, I did not perceive any additions of much importance to our previous knowledge. 5. Dr. Wollaston's elementary galvanic battery, described in a late number of the Annals of Philosophy, constitutes a discovery of considerable importance. It demonstrates the vast quantity of electricity which is disengaged during the chemical action of acids on metals, and thereby serves to throw much additional light upon the still obscure theory of galvanism. 6. I shall add here the result of Mr. Children's experiments with his immense galvanic battery, though they are mostly chemical; because I could not place them under the department of chemistry, without dividing them so much as to destroy their interest. The battery consisted of 20 pairs (or rather 20 triads) of copper and zinc plates, each six feet long by two feet eight inches broad. and presenting 32 feet of surface. They were connected together by leaden straps. Wooden troughs filled with water containing a mixture of sulphuric and nitric acids, and each water-tight, were prepared for each triad, and the metals were so suspended and counterpoised that they could be elevated and let down at pleasure. There were two copper plates in each cell, and the zinc plate was interposed between them. The order in which metallic wires connecting the two poles of this battery became red-hot was as follows: Platinum. Iron. Copper. Zinc. Silver. Tin and lead melting before they became red-hot their place. could not be determined. Mr. Children conceives that the metals conveying electricity become red-hot inversely as their conducting power. According to this supposition, the conducting power of these metals for electricity is in the following order : Silver. } Gold. Iron. The power of this immense battery may be estimated by the following experiments : Five feet six inches of platinum wire 0.11 inch in diameter were heated red-hot throughout visible in day-light. Eight feet six inches of a platinum wire 0.44 inch diameter were heated red. A bar of platinum of an inch square, and 2.25 inches long, was also heated red, and fused at the end. A round bar of platinum, 0.276 inch in diameter, and 2-5 inches in length, was heated bright red throughout. The chemical effects of this battery were as follows : (1.) Box-wood charcoal intensely ignited in chlorine produced no effect; nor was any effect produced in azotic gas. (2.) Oxide of tungsten fused, and was partly reduced. The metal greyish white, heavy, brilliant, and very brittle. (3.) Oxide of tantalum. A very small portion fused. The grains have a reddish yellow colour, and are extremely brittle. (4.) Oxide of uranium. Fused, but not reduced. (5.) Oxide of titanium. Fused, but not reduced. When intensely heated, it burnt, throwing off brilliant sparks like iron. (6.) Oxide of cerium. Fused; and when intensely heated, burnt with a large vivid white flame, and was partly volatilized. The fused oxide, when exposed to the air, fell to powder in a few hours. (7.) Oxide of molybdenum. Easily fused and reduced. The metal is brittle, steel-grey, and is soon covered with a thin coat of purple oxide. (8.) Compound ore of iridium and osmium, fused into a globule. (9.) Iridium, fused into an imperfect globule not free from cavities. The metal was white, very brilliant, and its specific gravity was 18.68. (10.) Ruby and sapphire were not melted. (11.) Blue spinell ran into a slag. (12.) Gadolinite fused into a globule. (13.) Magnesia was agglutinated. (14.) Zircon from Norway was imperfectly fused. (16.) Iron containing diamond was converted into steel, and the diamond disappeared. VI. MAGNETISM. 1. The magnetometer of Lampadius, described in the Annals of Philosophy (vol. iv. p. 434) may be of some use; and might perhaps be improved so as to renderit a tolerably correct instru ment. 2. It is well known that a magnetic needle, if it be poised exactly on a pivot before it receives the magnetic touch, will not retain the horizontal position after it has become a magnet. One end will incline more towards the earth than the other end. This is called the dip of the needle. It has been observed, that the end of the needle which is turned to the nearest pole is the one that dips, and the dip increases as we approach the pole, and diminishes as we approach the equator. The dip changes much more slowly There must be a mistake in this number. It represents the bar as smaller than the wire, of which eight feet six inches were heated red-hot. than the declination. Hence it would be of considerable importance to the theory of magnetism to be in possession of a set of good observations of the dip in different latitudes, and might lead to important deductions respecting the position and depth of the magnetic poles of the earth. On that account the following observations by Humboldt, giving the magnetic dip in different parts of the North Atlantic, for the year 1799, are of considerable value. 3. The variation of the compass, or the alteration which takes place in its declination, or in the point towards which it is directed in different longitudes, was first observed by Columbus. That the declination varies in the same place was first discovered in England, though the name of the discoverer is not accurately known. Wallis ascribes it to Gellibrand, who, according to him, made the discovery in 1645. According to Bond, the discovery was by Mr. John Mair. In the year 1657 there was no variation of the compass in London, or in other words, the needle pointed due north. In 1580 it pointed 11° 15′ east. In 1692 the variation was 6° west. Ever since the year 1657 the declination has been advancing west, and in the year 1814 it was 24° 22′ 22′′, according to a mean of the very accurate observations of Colonel Beaufoy, which I consider as superior in precision to any that were ever made before him. At first the declination varied at a considerable rate; thus, during the first 15 years after 1657, the declination had advanced west two degrees and a half, which gives a variation amounting to ten minutes for each year. But of late years this declination has been progressively diminishing, and according to the observations of Colonel Beaufoy, the increase from 1813 to 1814 was only 31"; or 40", if we confine ourselves to the state of the needle at noon. Dr. Halley was the first person who endeavoured to form a theory capable of explaining this variation in the declination. He supposed that the earth contained an immense magnet within it, poised upon its axis, and having four poles, two weaker than the |