plates at the distance of nine and four inches, and gave the deflecting forces in the ratio of 2 to 3, which are the square roots of 9 and 4. After trying the effects of the plates at different distances, the following law was established, which had formerly been obtained by a different process: viz.-that the quantity of Voltaic electricity circulating along the metallic conductor connecting two plates of dissimilar metals, is inversely as the square roots of the distances between the two plates. This law was originally deduced by Professor Cumming, by observing the deflection of a compass needle, and then taking the deflecting forces as the tangents of the angles of deviation from the original direction of the needle and straight conductor. When I undertook this investigation, it had escaped my memory that any law had been discovered which connected the deflecting force with the distance of the plates. This circumstance, as well as the different process by which it was deduced, affords the most complete proof of its truth.

This law is certainly very different from what we might at first have expected. We might, without experiment, have argued thus: If one inch of fluid between the plates offer a certain resistance to the electric current, two inches will present twice the resistance, three inches three times the resistance, &c. &c. With regard to the cause of this curious law, we can at present scarcely offer a conjecture. Does the electric fluid, after passing through a certain length of an imperfect conductor, acquire some power which enables it to pass more easily through an equal portion? There are phenomena in nature in which imponderable agents do acquire such proper ties. Light may be so far modified as to pass entirely through glass, which, without such a modification, would have been partly reflected. De Laroche discovered that invisible radiant heat, after passing through a thin plate of glass, passes with less resistance or loss through a second, &c. But, instead of being led away by analogies, which by some may be regarded as fanciful, I shall mention one practical lesson to be deduced from the law in question. In constructing a battery for electromagnetic purposes, there is not so much power gained as might be supposed by putting the plates very near each other. For example, if the plates are at the distance of a quarter of an

inch, and then at the distance of one-eighth of an inch, the power gained will only be as the square root of .25 to the square root of .125, or nearly as 50 to 35; and the hydrogen constantly escaping, and partially occupying the place of the liquid in the narrow cell, considerably diminishes this apparent increase of power. This circumstance ought not to escape the attention of philosophical instrument-makers in the construction of batteries for electro-magnetic purposes.

Considerable uncertainty still prevails with regard to the law which connects the conducting powers of metallic wires with their lengths. According to Professors Barlow and Cumming, the law is the same as that established for fluid conductors.

According to the experiments of M. Becquerel, the conducting powers of metallic wires are simply as their lengths. The following experiment will set the question at rest.

EXPERIMENT V.

The galvanometer I have hitherto used requires the following modification for this investigation. Form the rectangle of a single copper wire, and suspend the magnetic needle directly over it, and in the same direction. Take a certain length of the same copper wire, and connect it with a small elementary battery, turn the key, and observe the degree of torsion. Take nine times the length of the same wire, and repeat the experiment with the same battery and acid, and the number and degrees of torsion will only be one-third of those obtained in the first experiment. This experiment I repeated with different lengths of bell-wire, and always found that the intensity of the current was inversely as the square roots of the lengths -the same as the law for liquid imperfect conductors.

M. Becquerel seems to have fallen into the mistake we have now pointed out, by using a galvanometer made of a long wire formed into a coil, and neglecting the resistance the electric current must have experienced in passing through the instrument itself.

The conducting powers of metallic wires, or their ribands, for common electricity, depends almost entirely on their surface, without any reference to their thickness. The fact would seem to be, that common electricity glides along the surface of the

metal, being prevented from escaping by the pressure of the ambient air, whereas Voltaic electricity requires a certain thickness of metal for its transmission*. Voltaic electricity, from a single pair of plates, seems to be conducted from molecule to molecule, in some measure resembling the conduction of caloric. Hence, if the diameter of the wire be too fine to allow of this depth of metal, a considerable portion of the electric fluid will be stopped. But, provided the wires be sufficiently thick to allow of this necessary depth of the electric film, then the conducting power ought to be nearly as the circumference of the wire, or as its diameter. If one of the wires be very fine, and the other of a large diameter, this law could not exist. This fact was clearly proved by the following experiment.

EXPERIMENT VI.

Having taken equal lengths of very fine copper wire and of common bell wire, I used them successively as conductors from the same elementary battery, and ascertained the degrees of torsion as in the former experiments, and found that the large wire conducted better than in the mere ratio of the diameters. For example, the diameter of the one wire was scarcely three times that of the smaller, yet the ratio of their conducting powers was nearly as one to four. I then passed the thick wire through rollers, till it was reduced to a very thin riband, having its external surface nearly twice that of the original wire, but instead of conducting double the quantity of the original wire, it conducted only three-fourths of that quantity †.

From the law established in the fourth Experiment, we need scarcely despair of seeing the Electro-Magnetic Telegraph established for regular communication from one town to another, at a great distance. With a small battery, consisting of two plates an inch square, we can deflect finely-suspended needles

✦ Hence if a metallic rod be raised to a red heat, its power of conducting com mon electricity is increased, whilst its conducting power for Voltaic electricity is considerably diminished.

The fact here established bears a striking analogy to a curious fact discovered by Mr. Barlow. He found that it requires a certain thickness of iron or steel to receive the magnetic influence-Is there any relation between the thickness of the iron or steel necessary to receive the magnetic influence and the thickness of the conductor necessary to convey that kind of electricity which acts most powerfully on the needle ?

at the distance of several hundred feet, and consequently a battery of moderate power would act on needles at the distance of a mile, and a battery of ten times the power would deflect needles with the same force, at the distance of a hundred miles, and one of twenty times the force, at the distance of four hundred miles, provided the law we have established for distances of seventy or eighty feet hold equally with all distances what

ever.

PRACTICAL AND PHILOSOPHICAL OBSERVATIONS ON NATURAL WATERS.

BY WILLIAM WEST, Esq.

§ 1. On the Water from Peat Lands, and its application to domestic purposes.

I

HAD an opportunity, some time since, of closely examining many specimens of water from this part of the country, (Leeds,) which were soft and nearly pure, containing from half a grain to two grains of solid matter in the gallon, one part in 50 or 60,000, but tinged by colouring matter from peat. With most of the re-agents no action took place, or it was so slight as to be difficult of detection; but when evaporated until a gallon was reduced to a few spoonfuls, the composition of this small portion was easily shewn to be sufficiently complicated and it varied greatly in different specimens which, passing in their original state under the action of the tests without any alteration being produced, might have been supposed exactly similar. The fact is, the water precipitated from the rain and mountain mists had taken up small portions of the soluble substances which came in its way; but its course had been too short, and its action too much confined to the earth's surface, to acquire much from any of these. These streams were on high moor land; either running in the ravines, or springing from natural or artificial openings in mill-stone grit.

One practical difficulty of considerable importance arises when water from brooks in such situations is employed, or

when a large quantity of such water has to be collected for the supply of a town. The upland streams, deriving their supply from high and barren land, barren of all but moss and heather, are more or less deeply coloured by vegetable matter derived from peat. There has occasionally been much controversy respecting this peaty water; and among those who have entered keenly into this, both parties have been, I think, somewhat in the wrong. While those are mistaken who condemn, in the gross and for every purpose, water tinged in any degree with peat, or who maintain that it cannot be deprived of this colour, they are equally so who treat such an impregnation as not injurious to any of the useful qualities of the water. What may be the exact effect on the human constitution of the small quantity of soluble vegetable matter, of whatever nature, from which the hill streams derive their colour, I do not pretend to say; but the water is unsightly, not only from the brown tinge, but from the coloured froth formed by the bubbles of air which escape on standing. These, in water in general, break as they reach the surface; but, from the viscidity produced by the peat, they collect and remain, giving an unpleasant and repulsive appearance.

Now, I hold an opinion, which has been confirmed by some experienced medical men, that the salubrity of water, as a beverage, depends less upon its absolute purity than upon its being brisk and palatable. We know how palling to the stomach is water which has been boiled and cooled, or has stood long in open vessels; yet, so far as the term 'pure water' means water free from the presence of other substances than water, such is frequently more pure than when originally drawn. I apprehend, that though much in diet which is agreeable to the palate is at the same time unwholesome, yet that will not commonly perform its part well which is itself positively disagreeable.

Again, in experimenting upon this peaty colour, either as strong as it could be obtained, or in its common and more dilute state, I found it closely to follow the habits of those vegetable infusions which are prepared expressly for the colour they impart. Thus it is found dissolved, not merely suspended, passing any number of times through filtering-paper without