19345678DOIER; Degrees. length of the surface of the table, full size, will show its form, and the subjoined columns will supply the figures for the rest. Table of Degrees and Elevation to be marked on the Quadrant. Eighths. 12345 Inches Diameter. The table showing the height for every degree of elevation may, for the sake of expedition, be figured on the face of the Inches Circum- 4 quadrant. And, in practice, the instrument should be placed exactly fifty feet from the tree to be measured, the calculations being made for that distance; the quadrant is to be placed with the index at o, and the sights so as to form part of a line that will touch the left side of the tree at the place where the diameter is wanted; the degree of elevation being noted, the slider supporting the quadrant should be moved from left to right, till the sights on the quadrant form part of a line touching the opposite side of the tree. The space travelled over by the index will be the exact diameter, and on the opposite lines, on the near side, will be seen the corresponding circumference and side of the square; and at the same time, opposite to the degree of elevation, will be seen the height of the point where the diameter was taken. The following figure (6.) 6 will illustrate the mode of operation. The instrument is placed on an uneven surface fifty feet from the tree. The plumb of the quadrant touching o gives a level from the instrument, below which point the tree measures six feet. The first angle of elevation taken is 15°, which, by looking at the table on the quadrant, gives 13 feet 4 inches. The next angle is 25°, which gives 23 feet 3 inches, which, by subtracting the last height, leaves 9 feet 10 inches for the length of the intermediate piece. In the same way the length of the small piece between 25° and 36° will be easily found. The full height at 36° above the level of the instrument being 36 feet 3 inches, we have only to deduct the height at 25°, which leaves a difference of 13 feet 0 inches for the length of the piece. Opposite to 45° on the table I find 50 feet, being the height of the summit of the tree above the instrument, and which, added to the 6 feet below that level, gives the height of the tree, or 56 feet. The legs of the instrument, I should remark, are attached to it with thumbscrews. The single leg has a motion along, and the other two across the instrument, by which means it can be fixed to any level. A telescope attached to the quadrant with cross hairs, and a spirit level sunk in along the table, might be useful accompaniments, but are not indispensable. An index or arrow is placed at the off side of the slider, to mark the space travelled over in taking the diameter. Annat Garden, Feb. 24. 1826. An instrument for effecting the same objects as that of Mr. Gorrie, by nearly similar means, has lately been made the subject of a patent by Mr. James Rogers of Marlborough. It is termed an instrument for determining the angles, from the measure of the tangents of which the solid contents of standing timber may be ascertained. On some future occasion we shall give a description and figure of it; in the meantime, such as are curious in dendrometers, will find Mr. R.'s described in the Mechanics' Magazine, vol. vi. p. 295. It is certainly a most elegant instrument, but not more original and ingenious than that of our correspondent Mr. Gorrie.- Cond. ART. IV. Scheme of a Succession of Crops for One Hundred Acres of Arable Land in Picardy. By THOMAS BLAIKIE, Esq. C.M.H.S., &c. Landscape Gardener, Paris. Dear Sir, I HAVE received with pleasure your valuable work, the Gardener's Magazine, which is well known here, and read by M. Soulange Bodin, M. Cels, M. Boursault, and other eminent cultivators and amateurs. I shall be most happy to contribute to a work so truly devoted to our art, in every way in my power; and I now send you a farming scheme, made for the French government soon after the Revolution, with a view to show them how they might cultivate one hundred acres of land with only two horses. The Directoire approved of the system, and wished to have it published, as did my worthy friend, the late M. Thouin. It was then the custom in France to sow about seventy seeds to every square foot, and as I proposed to sow only one quarter of that quantity, the proposal was very acceptable to the Directory, who were in dread of a famine. Perhaps these tables may be useful to gardeners, who act also as farm managers for their employers; they will also afford hints to proprietors who farm their own lands, and to emigrants in the British colonies, how to regulate the distribution of labour, and raise abundance of forage for live stock, and consequently a large quantity of manure. In the months of December and January, which are generally frosty, the manure is carted upon the land, and the corn thrashed and laid in the granary, or taken to market. In the month of June the hay is made, and in July and August the corn is cut and stacked. In my next letter I shall give you some account of my life and gardening transactions for above three quarters of a century. I remain, dear Sir, &c. A Paris, Rue de Colisée, No. 23. July, 1826. THOMAS BLAIKIE. Tables referred to by Mr. Blaikie. Acres of Work necessary to be done in every Month in the Year. Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec. |