Beyond this inclination, the colours are no longer distinguishable. The whole series indicates a separation of the colours much more considerable than in the Scale of Newton; but to examine the variation of the polarizing energy for the several simple colours more minutely, we must have recourse to homogeneous light. The requisite measures were taken with every precaution in very fine sunshine, and though, owing to the imperfections of the specimen, they do not pretend to great precision, the resulting numbers can scarcely be erroneous to the extent of or of their own value. I think it necessary to premise this, as the law of action indicated by the following Table of the results is so very surprising and unexpected, that it was not without scrupulous examination I could persuade myself that no enormous oversight had been committed. The first column expresses the colour of the incident ray, the second the length of the shortest period of alternate polarization it is capable of performing within the crystal, computed by M. Biot's formula, lt. in which t represents the thickness of

sin . tan

n

the plate, the angle an intromitted ray makes with the axis (supposed perpendicular to the surface), n the number of periods and parts of a period it executes during its passage through the plate, or the order of the ring to which it is referred at its egress, and the length of a period performed by the same ray, supposed to traverse the crystal at right angles to its axis, or the minimum length above mentioned. The third column con

tains the value of, which measures the polarizing energy of the crystal on that particular ray; the last the number of observations employed in computing the values in the preceding.

TABLE III. Representing the Law of Action of the
Second Variety of Apophyllite, on the differently
coloured Rays of the Spectrum.

By this Table we see that the action of the crystal decreases rapidly, but regularly enough, from the extreme red to the blue rays, when it sinks all on a sudden, and throughout the whole extent of the indigo and first portions of the violet is so small, that I was unable to obtain a measure even of the first ring at its maximum, within the range of incidence my apparatus would admit. It then increases again, more suddenly than it fell, and for the extreme violet has a value intermediate between those for the yellow and green. If we construct a curve roygbiv, late VII. Fig. 14. whose abscissas AR, AO, &c. are reciprocally proportional to the lengths of the Newtonian fits, and drawing the line Ar B at an angle of 45° with AV, take the ordinates Rr, O o, &c. every where proportional to the value of in this Table, this curve will represent the action of this variety of apophyllite on the whole spectrum, while r B represents that of a crystal whose tints follow the Scale of Newton.

1000000

This is in perfect agreement with the succession of tints gi ven above. If we cast our eye over it, a deficiency of the indigo rays is perceived in all the scale of the extraordinary pencil, no pure or rich blue occurring throughout its whole extent. In the ordinary pencil, on the other hand, the excess of indigo appears

immediately in the rich tints of indigo, purple and crimson, which occur in the first order. The yellow rays, too, afford us a numerical verification of the number assigned to them. The maxima and minima of these coincide, as Newton has observed, with the most luminous, and obscurest parts of the rings, which is a necessary consequence of their great illuminating power. Now these occur at the incidences 23° 35′, 33° 2′, and 39° 41′ respectively; and if we compute the angles of refraction (4) corresponding to these, and take n successively, 1,, the formula already employed gives

which differs from the result in the third Table by less than of its value.

The absolute polarizing powers of the two portions into which the crystal was divided, differed no less remarkably than the characters of their tints. In the thicker plate, by a mean of 20 careful observations made by the interposition of a certain standard red glass, on the ring of the third order at its minimum, (in which the evanescence of the extraordinary pencil was complete,) I found 37° 3' for its apparent semi-diameter in air; and hence we find @=23° 7′, n=3, t=165900, which substituted give

and, (as is sufficiently evident from the scale of tints in this portion,) the value of l is nearly the same for all the other colours, Now it is well worthy of observation, that this value coincides almost precisely with the number similarly determined for the variety examined in my paper above alluded to, which I have there found to 9281. The difference is little more than

1

1000 of the whole, and so exact an agreement could hardly have been expected even in plates detached from the same specimen. This circumstance, together with the identity in the scale of tints exhibited by the two substances, establishes not only their exact similarity as individuals, but, what is of much more importance in this case, the definite nature of the variety itself;

and at the same time proves that in detaching the two portions from one another, no part of the second variety remained adhering to the first, as it must have become sensible by enfeebling the polarising power, if not by altering the tints.

(To be concluded in next Number.)

ART. XVI.—On the Antiseptic Power of the Pyrolignous Acid upon Fresh Meat, subjected to a Sea Voyage and a Hot Climate. By J. STANLEY, M.D. In a Letter to Dr BREWSTER.

As I am not aware that any experiments have as yet been published, wherein meat preserved by means of the pyrolignous acid was subjected to the test of a sea voyage and a hot climate, I have taken the liberty of sending you an account of the following trial, if you deem it worth your notice.

Having previously made several experiments with the above named acid, the results of which were favourable, on the 6th of October 1819, I prepared two pieces of fresh meat (beef) with the purified acid, applying it lightly over their surfaces by means of a small brush. After hanging up in my kitchen till the 12th of November following, I gave one of the specimens to the captain of a vessel bound for the West Indies, with directions to observe and note any change that might take place during his voyage, and to bring it back to me on the return of his ship to port. In the month of October 1820 he restored me the specimen. He had examined it several times on the voyage out, and during his stay of some months at the Island of Tobago, as did several gentlemen resident there, but no perceptible change could be detected. On comparing it with the specimen kept at home, I could observe no sensible difference in their appearance. On the 21st December following, I caused both to be thoroughly boiled, and, when served up, they were declared by several gentlemen who tasted them with me, to be perfectly fresh and sweet, and, with the addition of salt and vegetables, a palatable and wholesome dish.

The above experiment I think fully proves the antiseptic powers of the pyrolignous acid, my specimens having been preserved for the space of fourteen months, and one of them sub

jected to a long sea voyage, and the action of a West India climate, with success.

I have, for the purpose of verifying the foregoing experiment, again prepared two specimens, the one mutton and the other beef, and sent them out to the same island, with similar directions, and I make no doubt of the result being equally satisfactory. I remain, &c. J. STANLEY.

WHITEHAVEN, Feb. 7. 1821.

ART. XVII.-Notice of the Voyage of EDWARD Barnsfield, Master of his Majesty's Ship Andromache, to New South Shetland *.

ABOUT a twelvemonth ago, an English merchant brig, in performing a voyage to this port, made what they supposed to be land, several degrees to the southward of Cape Horn, and in a situation in which it is positively asserted that no land can exist. From the difference in opinion of those on board the vessel, and, from some other circumstances, little credit was attached to it at that time; but the master being fully convinced that what had been seen was actually land, determined to put it beyond a doubt, should he come round again. He accordingly made the land again last October, and having sailed along it for some considerable distance, he returned about the beginning of December to this port, and laid before the Naval Commander in Chief here, such charts and views, as induced him to hire the same brig on account of Government, to complete the discovery. The command of the expedition was given to Mr Edward Barnsfield, master of H. M. S. Andromache, with three midshipmen from the same ship, to assist him in his nautical researches; and as it was deemed necessary to send a medical officer, I went as a volunteer on the occasion. We sailed from Valparaiso on the 20th of December 1819, but did not arrive on cruising ground till the 16th of January 1820, having been almost constantly harassed with baffling winds and calms till we arrived in a high southern latitude. On that day, however, we had the good

See this Journal, vol. III. p. 367. particularly p. 374. and Plate XII. of that volume.