generally understood and adopted; whilst even within the memory of man, as was stated by an eminent member of your society at the last exhibition, whatever skill might have been attained in working with the dial, Cornwall did not furnish an artist capable of producing the instrument, which was not to be purchased in the whole county. The accuracy, beauty, and elegance, conspicuous in many of these instruments, made by Cornish artists and displayed in the Polytechnic Hall, clearly show that such a reproach no longer attaches to us; nay, more, instead of being dependent on other parts of the kingdom for philosophical and mechanical instruments, we are enabled to supply the most delicate and elaborate that can be required, even for the highest branches of scientific research and experiment."

We have marked for extract an interesting paper by Mr. Enys, on "Duty and Horse-power"-and various other articles which shall appear in our pages in due season. We take leave of the Report, wishing well to the Society, and trusting that our observations will be taken in good part, as we are assured, that if they are acted upon they will tend to the prosperity and increased usefulness of the Association.

ON A LARGE AND VERY SENSIBLE THERMOSCOPE GALVANOMETER. BY JOHN LOCKE, M.D., PROFESSOR OF CHEMISTRY IN THE MEDICAL COLLEGE OF OHIO.

[From the London and Edinburgh Phil. Mag.] The chief novelty of the instrument which I am about to describe, consists in its proportions and the resultant effects. The object which I proposed in its invention, was to construct a thermoscope so large that its indications might be conspicuously seen, on the lecture table, by a numerous assembly, and at the same time so delicate as to show extremely small changes of temperature. How far I have succeeded, will, in some measure, appear by a very popular, though not the most interesting experiment which may be performed with it. By means of the warmth of the finger applied to a single pair of bismuth and copper disks, there is transmitted a sufficient quantity of electricity to keep an eleven-inch needle, weighing an ounce and a half, in a continued revolution, the connexions and reversals being properly made at every half turn.

The greater part of this effect is due to the massiveness of the coil, which is made of a copper fillet about fifty feet long, one-fourth of an inch wide, and one-eighth of an inch thick, weighing between four and five pounds.

This coil is not made in a pile at the diame ter of the circle in which the needle is to revolve, but is spread out, the several turns lying side by side, and covering almost the whole of that circle above and below. The best idea. may be formed of the coil by the manner in which it is actually modelled by the workman. It is wound closely and in parallel turns on a circular piece of board eleven and a half inches in diameter, and half an inch in thickness, covering the whole of it except two small opposite segments, of about 90 degrees each. The board being extracted, leaves a cavity of its own shape to be occupied by the needle.

The copper fillet is not covered by silk, or otherwise coated for insulation, but the several turns of it are separated at their ends, by veneers of wood, just so far as to prevent contact throughout. In the spreading out and compression of the coil it is similar to Melloni's elegant apparatus, though in my isolated situation in the interior of America, I was not acquainted with the structure adopted in his prior invention. In the mas siveness of the coil, my instrument is, per haps, peculiar, and by this means it affords a free passage to currents of the most feeble intensity, enabling them to deflect a very heavy needle. The coil is supported on a wooden ring furnished with brass feet and levelling screws, and surrounded by a brass hoop with a flat glass top or cover, in the centre of which is inserted a brass tube for the suspension of the needle by a cocoon filament. The needle is the double astatic one of Nobili, each part being about eleven inches long, one-fourth wide, and one-fortieth in thickness. The lower part plays within the coil, and the upper one above it, and the thin white dial placed upon it, thus perform ing the office of a conspicuous index underneath the glass.

I have not yet made any very extensive experiments with this instrument, being only just prepared to do so. It is very sensible to a single pair of thermo-electric metals, to the action of which it seems peculiarly adapted; but the efficiency of such metals is increased by a repetition of the pairs, as in the thermo-pile of M. Melloni, especially if they be massive in proportion to the coil itself. With a battery of five pairs of bismuth and antimony, the needle was sensibly moved by the radiation from a person at the distance of twelve feet, without a reflector, the air being at the temperature of 72°.

In a recent interview with M. Melloni, to whose politeness I am much indebted, he expressed his opinion that with a thermopile, massive in proportion to the coil, my galvanometer might be made to exhibit his thermo-experiments advantageously to a large class. Some idea may be formed of

its fitness for this purpose from the result of a single trial on transmission. The heat from a small lamp with a reflector, at the distance of five feet, passed through a plate of alun, and falling on a battery or pile of five pairs of bismuth and antimony, deflected the needle only a fraction of one degree, but on substituting a similar plate of common salt, the same heat produced, by impulse, an immediate deflection of 33 degrees.

Although the instrument is finely adapted by its size for the purpose for which it was intended, class illustration, yet, from the weight of the needle, and the difficulty of bringing it to rest after it once acquires motion, it is not so suitable for experiments of research as the Mellonian galvanometer. When a massive thermo-pile, such as has lately been made by Watkins and Hill of Charing-cross, is connected with the coil and excited by a heat of about 200°, the needle being withdrawn a distinct report is obtained on interrupting the circuit; in producing this effect it is less efficient however than the ribbon coil of Professor Henry. The tube for suspension, placed over the centre of the instrument, is so constructed, as to admit of bing turned round by means of an index, which extends from it horizontally over the glass cover, and thus any degree of torsion may be given to the suspending filament or wire. A wire of any desired thickness may be easily substituted for the cocoon filament, when the instrument becomes adapted to measuring the deflecting forces of the galvanic battery. By using a thick wire it was ascertained that the calorimetor of Professor Hare, having forty plates, each 18 inches square, acted on the needle with a force equal to 92 grains, applied at the distance of six inches from the centre. In attempting to force the needle by torsion into a line parallel to the coil, where the deflecting current acts with the greatest strength, I accidentally carried it too far and reversed its position, when instantly it became reversed in polarity, that which had been the north pole becoming the south. This showed how unfit is the magnetic needle to measure such a quantity of electricity as was then flowing through the massive conductor. The instrument is well adapted to show to a class the experiments upon radiant heat with Pictet's conjugate reflectors, in which the differential, or air, thermometer

affords, to spectators at a distance, but an unsatisfactory indication. For this purpose, the electrical element necessary is merely a disk of bismuth as large as a shilling, soldered to a corresponding one of copper, blackened, and erected in the focus of the reflector, while conductors pass from each disk to the poles of the galvanometer. With this arrangement the heat of a non-luminous ball at the distance of 12 feet will impel the needle nearly 180°, and, if the connexions and reversals are properly made,will keep it in a continued revolution.

I have thus given you a brief sketch of an instrument which seems to supply a desideratum on the lecture-table, when the common thermometer is too small to afford to a class that direct and full satisfaction which, in a subject so important as that of heat, is very desirable to every professor. I have not, so far, attempted to use it extensively as an instrument of research, yet it shows evidently the importance of massiveness in conductors for feeble currents, such as those produced by thermo-combinations; nor am I certain that I have arrived at a maximum in this particular, for so far as I have proceeded in using thicker conductors for the coil, the deflecting effects have been increased.

London, August 30, 1837.

I am, &c.
JOHN LOCKE.

NOTES AND NOTICES.

Iron Welding.-A practice has for some time prevailed at Keswick, of welding iron and steel with a mineral which is said to be very abundant in that neighbourhood, and is found to answer the purpose much better than sand or borax, inasmuch as it affords a decidedly better protection to the fusing metals. It is used in the same common or simple way as sand, requiring no further care or management. Two, three, or more pieces of cast steel may be welded together, and drawn out, hardened, and broken across the junctures, which cannot be observed; or iron or cast steel can be welded together in the same way, as perfectly, and with as much ease as the mildest steel or iron.-Carlisle Patriot. Premium for Bottle-washing Measuring Machine. -Two or three of the designs offered seem of such equal merit, that it has been thought proper to make an actual trial of them, before deciding which is the best. We hope in a week or two to be able to announce the award of the premium.

Railway Map of England.-On the first of August will be published the Title, Index, and Contents to vol. 28 of the Mechanics' Magazine, and as a frontispiece to the volume a large map of the Railways in England and Wales, price 6d. The map alone on fine paper, price 6d. Also the volume complete, in half-cloth, price 8s. 6d.