made some

plates only are employed. Every practical electrician would however, I am convinced, refer the anomalous results of these experiments to some inaccuracy in the apparatus, or to a difference in the density of the fluid with which the batteries were charged; as the irregularities obtained were, by far too considerable, to have been produced by a difference so trivial as that existing between the number of plates employed on this occasion. The authority of a philoso pher, so highly and so justly celebrated as Dr. Davy, may give extensive and respectable circulation to even palpable errours; it is therefore the imperative duty of every genuine friend of science, to examine assertions flowing from such a source, and to give to the public any facts he may be acquainted with, that militate against, or contradict them." Experiments As early as the year 1804, direct experiments were made on the subject to ascertain the quantity of wire ignited by different numis bers of plates. Of this I presume Dr. Davy was not aware, when he stated, that "the inquiry had not yet been touched on;" he may not have read the 18th volume of the Philo sophical Magazine, or the 7th and 8th volume of Mr. Nicholson's Journal, or Cuthbertson's Practical Electricity, where an account of these experiments is published. In the 7th volume of this Journal, page 207, a series of expe riments with large batteries of plates of 4 inches, and of The power of 8 inches square, is detailed by Dr. Wilkinson: the results direct ratio of of these experiments prove, that the power of ignition in the plates. creases in direct proportion to the number of plates employed; and this law of increase is uniform, whatever be the size of the plates. If a battery of any given size melt any deters minate length of wire, two such batteries will melt twice the length, three such batteries will treble the effect, and by four it will be quadrupled, provided the acid with which they are charged is of equal strength.

years ago.

Other experiments gave si milar results,

In the 8th volume of this Journal, pages 97 and 205, very accurate series of experiments is given by Mr. Cuthbertson. By a variety of trials he proves, that double the quantity of plates burns twice the length of wire; and he points this out as a distinction between the action of common and Voltaie electricity, but concludes, that the dif ference arises from the imperfection of the Voltaic appara

tus;

tus; as on one occasion he obtained a different result by with one ex. ception. employing very large plates arranged as a pile. In subse quent volumes of this Journal are several other papers on the same subject; but enough has been quoted to show, that the inquiry has not any claim to originality. The conclusions of the first experimenters are however at variance with those of Dr. Davy. Dr. Wilkinson and Mr. Cuthbertson suppose, that the igniting power of a battery com posed of plates of any given size increases in direct proportion to the number of plates. Dr. Davy infers from his experiments, that, when a few plates are increased, the increase is as the square of the numbers; but in combinations of greater extent the effect does not increase ao rapidly. The apparatus employed by Dr. Davy differs in structure As the apparafrom that of the earlier experimenters; and as this might occasion some slight difference in the results, I did not consider it justifiable to decide on the accuracy of either, with out new trials. With the assistance of Mr. Cuthbertson the experithe following experiments were made; their results furnish some useful practical information in addition to the ascer tainment of the object, for which they were expressly insti tuted.

tus was not the

same,

ments were

repeated.

The acid mixture employed to charge the batteries was The acid emof the same strength in all the experiments, (being pre- ployed. viously mixed in a large vessel for this purpose). It consisted of 10 gallons of water, 5 lbs. of strong nitrous acid, and half a lb. of muriatic acid. A mixture of this kind being the most effectual wire-melting charge. Ten bat. The apparatus. teries, each containing 10 pairs of four inch plates, fitted up in troughs of Wedgwood ware; and one battery, of 50 pairs of plates of the same size, fitted up in a wooden trough, with glass partitions, constituted the apparatus employed. The plates in the troughs of Wedgwood ware were new, but the glass partitioned battery had been fre quently employed before.

Two of the Wedgwood batteries rendered nine inches of Exp, 1. iron wire, T of an inch diameter, faintly red hot, when the contact was first made. This effect continued but a very short time. When it had wholly ceased, an interval of one minute was suffered to elapse, and at the end of this

Exp. 2.

Exp. 3.

Remarks.

Exp. 4.

Exp. 5.

Exp. 6.

tion to the

time the contact was again made. Three inches of the same wire were now rendered red hot with the same appearance as the nine inches in the first experiment.

Four Wedgwood batteries were next employed. At the first contact 18 inches of the same wire became slightly red hot; and the contact was preserved, till the effect of igni tion entirely terminated. One minute was suffered to elapse, when, on removing the contact, 6 inches of wire were ignited in the same degree as in the preceding experi

ments.

An interval of three minutes was suffered to pass without contact; at the end of this time, two batteries rendered six inches of the same wire red hot, and four batteries produced a similar effect on 12 inches.

The uniform result of these experiments, in which the igniting power increases in the same proportion, however variable the action of the battery, renders it highly probable, that in Dr. Davy's experiments the batteries were accidentally charged with acid mixtures of variable strength, the increase in his first experiment being as the square of

the numbers.^

To ascertain whether the ratio of increase continued the same when a larger combination is employed, ten batteries were charged with fresh acid, of the same strength. Five of these ignited at the first contact 18 inches of the same wire as that employed in the former experiments; and on repeating the experiment with ten batteries, an effect precisely similar was produc d on 36 inches.

A short interval was suffered to elapse, when five batteries ignited 15 inches of wire; and the same effect was produced on 30 inches by ten batteries.

Platina wire, th of an inch diameter, was taken. Ten batteries (in a diminished state of action) maintained a white beat in 5 inches of this wire. On repeating the experiment with five batteries a similar effect was produced on 22 inches of the same wire.

The power in These experiments indicate, that the conclusions of Dr. direct propor- Wilkinson and Mr. Cuthbertson are legitimate; and they prove also, that the igniting power not only increases in exact proportion to the number of plates; but that this ratio of

number.

increase

increase is uniform, however variable the action of the batteries may be.

ance of the

size of the

The troughs of Wedgwood ware have the partitions, The continu which form their cells, at à greater distance from each other, action depends than that of the glass partitions in the wooden trough; they more on the of course require more acid to excite a given quantity of acid than the plates; and it has been said, that this circumstance promotes cells. the continuance of their action. The results of my experiments speak a different language. The continuance of the action is influenced much more by the nature and strength of the acid mixture; and I have not observed, that in any case the separation of the partitions to a greater distance than ths of an inch is attended with any advantage in this respect.

At the commencement of the preceding experiments, a Glass partitiglass partitioned battery, of 50 pairs of four-inch plates, oned battery. was filled with the same acid mixture as that employed in the troughs of Wedgwood ware. Its action was greatly inferior, in consequence of the oxidated state of the plates from former operations; but the continuance of its action appeared precisely similar, and at the conclusion of the experiments the effects were so nearly alike, as to admit of no perceptible distinction. At the first contact 9 inches of wire were ignited, and by allowing an interval of five mi nutes a similar effect was produced by a second contact; a Batteries recircumstance which proves, that the voltaic battery requires, quire time to produce their like the electrical machine, time to produce its full effect. full effect. This fact, as indicated by the sensation produced on the animal organs by a series of 600 small plates, was noticed many years ago by Dr. Wilkinson,

The preceding are part only of a series of inquies on this subject, which have long occupied my attention, and which I purpose to detail in future numbers of the Journal; anxious only, that in experimental science assertions be supported by accurate experiments; and that, in the progress of philosophical discovery, the merit of the first labourers be not forgotten amidst the achievements of their successors. No. 3, Princes Street, Cavendish Square,

April the 13th, 1811.

VOL. XXIX.-MAY, 1811.

D

IV.

connecting the

poles of a horseshoe magnet adhered with

IV.

On the different Forces with which Tubes, Bars, and Cylinders, adhere to a Magnet. In a Letter from Mr. E. LYDIATT.

SIR,

THROUG

.

To Mr. NICHOLSON.

HROUGH the medium of your scientific Journal I am anxious to obtain information on some magnetic phenomena, which I have lately noticed to have taken place on applying different shaped conductors to connect the poles of a horseshoe magnet.

In preparing the introductory course of lectures on the An iron tube philosophy of the mechanic arts, which I have delivered this season at the Scientific Institution, I had occasion to make few experiments on the magnetic property of iron and steel; in the course of which 1.happened to place a piece of iron great force.tube in contact with the two poles of a horseshoe magnet composed of thin bars; and found to my surprise, when I attempted to remove it, that a considerably greater force was required, than that necessary to separate the conductor which belongs to the magnet, which, as usual, was a square piece of iron with a ring attached, and presenting a flat surface equal to the combined polar surfaces of the three bars composing the magnet. This striking singularity induced me to ascertain the relative force required, to overcome the different degree of attraction.

that of a bar as $3 to 10.

I first applied the conductor belonging to the magnet, Its adhesion to and, by suspending weights from the ring, found, that it separated with 5lb. I then supplied its place with the tube, which was a piece of gun-barrel about two inches in length, attached longitudinally from one pole to the other; and by passing a wire through it, and twisting the two extremities into a hook, I suspended the weights, and found that 111b were requisite to separate it from the magnet. From this experiment it will be evident, that the relative degree of attractive force, exerted by the magnet on these two different conductors, is as 10 to 23. I repeated the experiment several times, and the results were invariably the same.

The