the road. We paid visits to several of them. In one of them, containing not more than four tents, we found only women, who were busy in distilling brandy from milk. The women confirmed what we had been before told concerning the materials used for distilling, and said that, having made butter, they were distilling the butter-milk for brandy. We could not credit that brandy might be so obtained; but to prove it, they tapped the still as upon a former occasion, offering us a tuft of camel's hair soaked in brandy, that we might taste, and be convinced.

III. Proposed Mineral Surveys of the British Counties. Mr. KIRWAN'S Opinions on this Subject.

It appears to have been the original intention of the Pre

sident and Members of the Board of Agriculture to ascer tain,

"1. The riches to be obtained from the surface of the national territory.

2. The mineral or subterraneous treasures of which the country is possessed.

3. The wealth to be derived from its streams, rivers, canals, inland navigations, coasts, and fisheries; and 4. The means of promoting the improvement of the people in regard to their health, industry and morals, founded on a statistical survey, or minute and careful inquiry into the actual state of every parochial district in the kingdom, and the circumstances of its inhabitants."

Conceiving, that under one or other of these heads, every point of real importance, that can tend to promote the general happiness of a great nation, will be included.

The first point, viz. the cultivation of the surface, and the resources to be derived from it, appearing to have a prior claim on the attention of the Board, it has been particularly kept in view in the selection of their surveyors or reporters, and in the instructions given to these gentlemen, who have done themselves so much credit, and the country so much service, by the many able county reports which they have enabled the Board to present to the public; in which reports, the three latter subjects are only incidentally touched upon, although much valuable matter has been collected and published relating to them, on the two latter heads in particular. The second head, that of mineral surveys, appeared of such a distinct nature, and of so much importance, to be entered on, when the agricultural part of their surveys

was

was accomplished, (which appears now to be almost the case) that the Board consulted several eminent mineralogists, as to the proper heads of inquiry, and on the best manner of conducting mineral county surveys; among whom was Mr. Richard Kirwan, and whose reply to the inquiries of the President on these heads is printed in the first volume of their "Communications," appendix lxviii.

I conceive that I shall be forwarding the very important objects of the Board, in giving a place to this letter of Mr. Kirwan. EDITOR.

"SIR, WHEN last I had the honour of meeting you in London, you were pleased to express a wish, that in order to promote a mineralogical survey of the kingdom, the proper objects of inquiry in every county should be briefly pointed out, and in such a manner as that they may easily be discerned, even by such persons as cannot be supposed to be deeply versed in such matters. In compliance with your wishes, I now send you the principal heads of such inquiries, many of which may be satisfactorily answered by architects, common land surveyors, masons, and even common labourers; though it were to be wished that persons of still superior education, as those of the clerical and medical professions, were also consulted. In the mining counties in particular, as Cornwall, Derbyshire, Flintshire, Devonshire, Lancashire, &c. the overseers of the works could give the best information; in many, several private gentlemen are known to be well instructed in those matters.

1st. Are there any mountains in that county? and their names? what is their course or direction? their height, known or reputed? whether of steep or gentle ascent, cultivated, woody, or otherwise? dry, or abounding in springs? in continued ridges, or separate and distinct? what sort of stone are they formed of (whether at the top, middle or bottom? what is their inclination) or is found in them? as granite, sandstone, whin, limestone, marble, alabaster, Derbyshire-spar, freestone, flags, slates, gravel, flint, &c., are they solid or cavernous? are they single, or one within the other? and the different stones in each? What other hills or eminences are there? of what composed? stony or chalky, and their direction and bearings, with respect to the mountains?

2dly. What rivers traverse the county? their names, length, breadth, depth, and direction? what lesser streams How into them, and their direction? temporary or perennial,

apt

apt to overflow, or otherwise? what lakes, and their ex tent?

3dly. What, or do any, mineral springs occur, in any or what parishes, and what is their nature, if known? by whom examined, and when?

4thly. What sort of stone commonly occurs in different parishes, in the plains, in sand-pits, making of roads, for buildings, mill-stones, &c., and what quarries?

5thly. What are the different soils that occur in different parishes, as clays, marles, sands, loams? are these last clayey, or sandy, or chalky? what mosses? do they yield peat? have brick-clay, fire-clay, potters-clay, terras, fuller's-earths, tripoli, &c. been found?

6thly. What mines are found in the country? whether metallic, or saline, or coaly? whether in veins, beds or bellies? their inclination and direction, or bearing? how is the ore raised? where are the ores worked, and the general mode of smelting them? were any, and what improvements lately made in the manner of draining them, freeing them from water, working or smelting them? are there any still required? have all the hills and mountains been yet examined, with regard to their mineral contents?

7thly. Have any collections or cabinets of the fossils of each county as yet been formed? let samples of each, docketed, with the name of the place in which it was found, be sent.

Much information, relative to these inquiries, may be found in the Philosophical Transactions, histories of particular shires and counties, as Cornwall, Derbyshire, &c.; tours through England, Wales, and Scotland, the works of Woodward.

A committee may perhaps be named, to examine these and arrange the particulars found in each shire, which might perhaps help the persons, to whom queries are to be addressed, to recollect and find them.

These are the particulars which at present occur to me : they may be digested, enlarged, and perhaps better methodized, in a committee. When answers are had, which at furthest may be in a year or two, a mineralogical map of the kingdom may be formed, serving as a fund of information, and a ground of future improvements in agriculture, commerce, and all the arts. I have the honour to be

Dublin, Nov. 17, 1795.

Your very obedient and humble servant,
R. KIRWAN."

To Sir John Sinclair, Bart. &c. &c.

IV. Memoir

IV. Memoir on the Diminution of the Obliquity of the Ecliptic, as resulting from ancient Observations. By M. LAPLACE. Translated from the "Connoissance des Tems for 1811" by THOMAS FIRMINGER, Esq.

[Concluded from vol. xxxvi. p. 434.]

Greek Observations.

PYTHEAS' observation at Marseilles was made between the two epochas of the preceding observations. In the second book of his Geography, and the 4th chapter, Strabo says: According to Hyppacus, at Byzantium, the proportion of the gnomon's shadow is the same as Pytheas pretends to have observed at Marseilles ;" and in the 5th chapter of the same book he adds, " at Byzantium, in the summer solstice, the proportion of the gnomon's shadow is 42 to

120."

It was no doubt from that observation that Ptolemy, in his Almagestes (b. xii. ch. vi.), draws through Marseilles the 14th parallel, in which the shadow's length at the summer solstice is 20% parts, the gnomon's being 60 parts. Pytheas was, at latest, contemporary with Aristotle; therefore his observation may, without any sensible error, be referred to the year 350 before our æra. After correcting it with the refraction and parallax, it gives 19° 28' 29" for the distance of the sun's centre at the solstice, to the zenith of Marseilles. The latitude of that town's observatory is 43° 17′ 49", from which if the preceding distance is subtracted, we shall have 23° 49' 20" for the ecliptic's obliquity in Pytheas' time.

The new Solar Tables, published by the Board of Longitude, which are founded on the formulas on book vi. chap. xii. of Méc. Cél. give 23° 46′ 7′′ for the ecliptic's obliquity, corresponding to the year 350 before our æra; the difference 3' 13" is within the limits of errors of which Pytheas' observation is susceptible.

About a century later than Pytheas' observation, Eratosthenes undertook to measure the earth, and founded that measurement on solstitial observations of the gnomon made at Syena and Alexandria. (Cleomedes, b. i. On contemplation of Celestial Bodies, ch. x. Of the Earth's Magnitude.) Eratosthenes made use of a vertical gnomon raised in a spherical segment. The summit of the gnomon being in the centre of the segment, he found the distance between the zeniths of Syena and Alexandria to be equal to a 50th

part

part of the circumference. Thus, according to this astronomer, the sun being at the zenith of Syena at the summer solstice, he found on the same day its distance from the zenith of Alexandria 7° 12'. This distance was from the upper edge of the sun; for the ancient astronomers did not correct the sun's altitude as observed by the gnomon, to obtain that of the sun's centre: which is the reason why their latitudes were too small by the apparent diameter of the sun. This is evident for Alexandria, whose latitude is calculated by Ptolomy at 30° 58'; while, according to Nouet's observations, it is 31° 13' 15"; greater therefore by 15' 5", which is nearly the sun's semi-diameter. The apparent altitude of the sun at the summer solstice at Alexandria, as observed by Eratosthenes, must then be corrected by the sun's semi-diameter, the refraction and parallax; which gives 7° 27′ 50′′ for the distance from the sun's centre to the zenith of Alexandria at the said solstice. Subtracting it from the latitude of Alexandria, as observed by Nouet, the difference 23° 45' 7" will be the obliquity of the ecliptic in Eratosthenes's time, or towards the year 250 hefore our æra. According to the formulas of Mec. Cél. it was at that epocha 23° 45′ 19′′, which agrees remarkably well with Eratosthenes's observations. These observations, together with Pytheas' and the preceding Chinese, all combine therefore to show that the ecliptic's obliquity, previous to our æra, was very nearly the same as is given by the formulas of Méc. Cél. Let us now consider the observations made since the commencement of our æra.

OF ANCIENT OBSERVATIONS POSTERIOR TO OUR ÆRA.

Chinese Observations.

The first of these observations dates from the year 173 of Our æra. It is recorded as follows, in Father Gaubi's MS. (Conn. des Tems for 1809, p. 395.)

"On the 9th of October 173. at Loyang, meridian shadow ten feet. On the 7th of February 174, meridian shadow nine feet six inches. These shadows were observed carefully."

The gnomon was eight feet long.

The altitude of the sun's centre resulting from the first shadow is 38° 22' 15", after being corrected by refraction and parallax. The one resulting from the later shadow, also corrected, is 39° 31' 9",4. Let x be the altitude of the equator at Loyang. If we calculate from the new Tables of the Sun just published by the Board of Longitude, the

sun's