2. On the existence of Pyro-electricity in Artificial Crystals.

It does not appear from any of Haüy's writings, that he even suspected the existence of pyro-electricity in crystals formed by aqueous solution. In subjecting some of these to experiment, I was surprised to find that they possessed this property, and some of them to a considerable degree. The following is a list of those in which I discovered it:

Among the preceding crystals, the tartrate of potash and soda, and the tartaric acid, are pyro-electrical in a very consis derable degree; but the action of several of the other salts is comparatively feeble.

3. On the Pyro-electricity of the Powder of Tourmaline.

Among the curious properties of artificial magnets, none is more remarkable than that which is exhibited, by cutting a piece from one of their extremities. If the piece is taken from the north pole of the magnet, it is itself a regular magnet, with north and south polarity. The very same property was discovered in the tourmaline by Mr. Canton, who found that, if it was broken into two parts when in a state of excitation by heat, each fragment had two opposite poles. Coulomb has ingeniously explained the magnetical fact, by supposing that each particle of the magnet is itself a magnet with opposite polarities; and Haüy has applied the same explanation to the analogous phenomena in the tourmaline.

If we attempt, however, to reduce the magnet into minute portions by any mechanical operation, such as filing, pounding, &c. the particles of steel are found to be deprived of their magnetical qualities, their coercive power being destroyed by the vibrations or concussions which are inseparable from the process of comminution. Analogy would lead us to expect the same result with the tourmaline; and we have no doubt that most philosophers, confiding in the force of recognised analo

gies, would expect that the powder or dust of pounded tourmaline would not exhibit any pyro-electrical phenomena.

In order to ascertain this point, I pounded a portion of a large opaque tourmaline in a steel mortar, till it was reduced to the finest dust. I then placed the powder upon a plate of glass, from which it slipped off, by inclining the glass, like all other hard powders, without exhibiting any symptoms of cohesion either with the glass or with its own particles. When the glass was heated to the proper temperature, the powder stuck to the glass; and when stirred with any dry substance, it collected in masses, and adhered powerfully to the substance with which it was stirred. This viscidity as it were, or disposition to form clotted masses, diminished with the heat, and at the ordinary temperature of the atmosphere it recovered its usual want of coherence.

Hence it follows, that the tourmaline preserves its pyroelectricity even in the state of the finest dust, and that this dust, when heated, is an universally attractible powder, which adheres to all bodies whatever.

This singular breach of analogy between the distribution of the pyro-electrical and magnetical forces, has an exact counterpart in the distribution of the doubly refracting forces in regularly crystallized bodies, and in plates of glass that have been rapidly cooled from a red heat. If a crystal of calcareous spar is broken into a thousand fragments, the most minute fragment possesses in miniature the same doubly refracting structure as the largest rhomb of that mineral; whereas the plate of glass that has derived its doubly refracting structure from rapid cooling, comports itself exactly like a magnetised bar of steel. Any considerable portion of the glass, though cut from the positive part, acquires, upon its being detached from the plate, both the positive and the negative structure; but if it is reduced to very minute fragments, or pounded, these fragments lose their doubly refracting structure ;-that is, any number of small fragments put together after separation, have not the same doubly refracting force as when they formed part of the plate, the loss of the doubly refracting structure always increasing with the minuteness of the subdivision.

This striking analogy between the effects of the electrical VOL. I. NO. II. OCT. 1824.

and doubly refracting forces, acquires a new interest from the known relations between the forces of electricity and magnetism, and is well worthy of being pursued into all its recesses. In a paper, which will appear in an early number of this Journal, I shall have occasion to point out many close analogies between the phenomena of magnetism and double refraction, which may help to throw light upon the physical principles which have created so many points of resemblance among the phenomena of the three sciences.

4. On the Pyro-Electricity of the Powder of Scolezite and Mesolite, when deprived of their water of Crystallization.

As the powder of Tourmaline, with which the preceding experiments were made, suffered no chemical change by trituration, I was desirous of trying whether or not the pyro-electricity of minerals existed, when the mineral was deprived of any of its ingredients. For this purpose, I converted several crystals of Scolezite and Mesolite into a white powder by heat, so as to deprive them of their water of crystallization, which is now considered as an essential ingredient in any mineral species. When the powder was exposed to heat, upon a plate of glass, it adhered to it like the powder of Tourmaline, and when stirred about by any substance whatever, it collected in masses like new-fallen snow, and adhered to the body that was employed to displace it.

This fact is a very instructive one, and could scarcely have been anticipated. As several minerals differ only in the quantity of their water of crystallization, the powder which was thus pyro-electrical, could not be considered either as Scolezite or Mesolite, but as another substance not recognised in Mineralogy. The pyro-electrical property, therefore, developed by the powder, cannot be regarded as a property of the minerals of which the powder formed a part, but merely as a property of some of their ingredients. In which of the ingredients, or in what combination of them the pyro-electricity resides, may be easily determined by farther experiments.

5. On the probable influence of Crystallographic composition on the distribution of Electricity in Minerals.

Although I have not been fortunate enough to meet with any of those crystals which are necessary in the investigation

of this branch of the subject, yet there are some facts of sufficient importance to be noticed in such an inquiry.

The Abbé Haüy has particularly mentioned* a crystal of topaz, in which the pyro-electricity was distributed in a very remarkable manner. He observed that its two extremities were both resinous poles, while the intermediate part gave indications of vitreous electricity. As this phenomenon has been observed only in one mineral, and in one specimen of that mineral, and as it has an exact counterpart in the phenomena of magnetism and of double refraction, it is very probable that the crystal in which it was observed was a compound crystal, in which the two vitreous poles were in contact.

Although the Scolezite and Mesolite are both composite minerals, yet the faces of composition are parallel to the axis of the prism, and therefore cannot affect the distribution of the electricity which is excited by heat. It is therefore in the topaz, and some of the other pyro-electrical minerals, where we must study the influence of composition.†

ALLERLY, August 2, 1824.

ART. III.—Journal of an Excursion through the Himalayah Mountains, from Shipke to the Frontiers of Chinese Tartary. By ALEXANDER GERARD, Esq. Surveyor to the Board of Commissioners, Lieut. and Adj. 2d Battalion 13th Regt. Native Infantry, on the Bengal Establishment. Communicated by the late Colonel GERARD of Rochsoles. Concluded from page

51.

After crossing the Darboong by a good sango, we marched on the 25th Oct. to Lubrung, a distance of 10 miles. The road was good, winding very much, and crossing the Roonung Pass, 14,508 feet high, at the top of which the wind was as strong

* Traité de Mineralogie, 2d edit. tome ii. p. 154. We hope that this crystal. is in the possession of the Duke of Buckingham, who, we understand has acquired the splendid cabinet of the Abbé Hauy.

+ Another example of the probable influence of structure on the developement of electricity exists in the Analcime, where the feeble production of electrici.. ty by friction, from which Hauy has derived the name of the mineral, is probably owing to its singular mechanical structure. See Edinburgh Transactions, vol. x. p. 187, 193.

and as cold as it was yesterday at Hungrung Pass. We found a great deal of juniper on the way, the berries of which were large and well tasted, having little bitterness.

Lubrung is a large village, on the right bank of the Zong rivulet, a couple of miles from the Sutluj, and 9296 feet above the level of the sea. Opposite to it, and a mile distant, is the populous town of Kanum, where Loktus resides during the winter season. There are two brothers of the names of Buleeram and Busuntram; but they are both generally called Loktus, which word, properly speaking, should be applied to their house, which is a building of great extent.

We marched on the 26th Oct. to Leepe, 6 miles. The road was bad, lying over sharp rocks. The houses here, as well as at Subrung, are wholly composed of wood. They are small, and in shape exactly resemble cisterns. Leepe consists of an upand lower division, both of which contain a good many per inhabitants. It lies upon the left bank of the Tetee, a large stream, having its source amongst snow twelve or fifteen miles to the north-west. The vineyards here are numerous, and the grapes large and of a delicious flavour.

We marched on the 27th Oct. to Akpa, 103 miles. The road was rocky, passing the village of Jaugee, and for the last four miles leading through forests of pine upon the left bank of the Sutluj, from which it was about a mile distant.

Next day we proceeded to Pungee, 10 miles. The foot-path was rugged in the extreme, passing great part of the way over fragments of granite, gneiss, and quartz, which appeared to have but recently fallen, and exhibited a heap of gigantic ruins, amidst which we saw many a noble pine lying prostrate, while a few, with their branches broken off, and otherwise disfigured, just barely peeped above the stones. Large portions of rock fall every year, and their ravages are truly dreadful. They sweep every thing along with them, and sometimes stop up the channels of the largest rivers for whole weeks.

From Leepe to this place there is a direct road not exceeding fourteen miles, but we chose to go round by the Sutluj, in order to have a view of the Kylas Peaks.

On the 29th Oct. we marched to Rogee, nine miles. The road was first a very steep descent of 1000 feet to the Mulgoon, a large stream descending at a considerable angle, rushing over