mended by Knight, for ripening grapes in July; say at London, we have Latitude of London 51° 29' Sun's declination on 21st July.. 17° 31′ See 33° 58' or 34° nearly, page 66 for the parts of a degree. Wilkinson adds that as we want the genial warmth of the sun most in spring, therefere, for general purposes, that construction would perhaps be best which gives us the greatest quantity of perpendicular rays then. If the inclination were 45°, the sun's rays would be perpendicular about April 6th and September 4th. As the rays would vary very little from the perpendicular for several days before and after the 6th of April and September 4th, the loss of rays arising from reflection would be nearly a minimum. My friend Mr. Caie gave us the following details in 1841, at a meeting of the West London Gardeners' Association. for Mutual Instruction, that in the construction of forcinghouses the proper angles could be selected to suit the period intended for producing each particular crop, and to be adapted for different latitudes to receive the most vertical rays of the sun for ripening the fruit. The Sun's Declination in each Month. Deg. Min. 21st of January the declination is South.. 19 52 When the sun has a north declination, or is north of the equator, From the degree of latitude, say 52 0 Subtract the sun's declination, suppose 23 30 The remainder gives the angle required. 28 30 When the sun has a south declination, or is south of the equator, To the degree of latitude. 52 0 Add the sun's declination, suppose about 23 30 75 30 The remainder gives the angle required N.B. The degree of latitude must be that of the place where it is intended to erect the horticultural buildings. I will now conclude this evening's lesson, leaving you to turn to some of the plans &c., in the Gardener's Chronicle and Journal of Horticulture, or to the buildings themselves to copy, should you, as I trust you will, have imbibed from my instructions this evening, some relish for the study. Land Surveying. Mr. B. Another method of surveying a triangular field is by measuring the three sides separately. The rule for finding the content by the pen is: From half the sum of the three sides, subtract each side severally, then multiply the half sum and the three remainders together, and the square root of the last product will be the content. Example: Suppose the sides to be 7 chains 15 links, 9 chains 50 links, and 12 chains 15 links; required the con tent. PROBLEM VI. To measure and find the content of a four-sided field. The method of measuring a field having four unequal sides, is, by measuring a line from one corner to the opposite one, and which is called a diagonal. This line divides the field into two triangles, to which it serves as a common base ; and the perpendiculars from the opposite corners, upon the base, must be measured as directed in the other problem. To find the content. Rule: Add the two perpendiculars together and multiply their sum by the diagonal, then half the product will be the To measure the content of a garden or of any other piece of ground having more than four sides. Any piece of land, bounded by more than four sides may be surveyed, by dividing it into triangles and trapeziums, and measuring the diagonals and perpendiculars. To effect which you must begin at some corner of the garden, or other piece of ground, and measure the several diagonals and per pendiculars as directed in the preceding problems, always remembering to leave a mark at the place where you begin, and at such other stations as may be necessary for distinguishing those parts that have been measured from those which have not, so as no part may be omitted, nor any part measured twice. The area of each triangle and trapezium must then be computed separately, by the pen, according to the rules in the preceding problems; and the sum of those areas will be the content required. In surveying a piece of ground by measuring the diagonals, it is best to make choice of the longest diagonals for the base lines, for the perpendiculars will be shorter, and the places they should rise from more easily found. On the contrary, the more remote any angle of the triangle is from the base line, the more difficult and the less certainty there is in obtaining the exact place where the perpendicular should rise from, as every practical surveyor can testify; and if you are only a yard wide of the true place, you will make the land more than it really is. It is indeed remarkable in practical surveying, that if a parcel of land be often measured, there will always be some slight difference, more or less, in the results. Some surveyors, for the purpose of planning or mapping, take severally the quantity of the angles contained by every two adjacent sides in the field; in this case they measure both the sides and the angles regularly round the field. To perform this operation with the chain only, without the assistance of an instrument for taking angles, you must begin at the corner *where you intend your first angular point to be and from thence, measure two chains in a right line with the mark at the corner you intend to go first to, or in the direction of the line you intend to measure first; and at the end of the two chains stick down an arrow. In like manner measure from the same corner two chains in a right line with your last station, or in the direction of the line which you intend to measure last; and at the end of the two chains, put down another arrow. Then if the distance between these two arrows be measured to the nearest inch, it will be the chord line to the angle sought, and must accordingly be entered in the field book before you proceed to measure the length of the next hedge. You must thus proceed with measuring the intercepted angles and the length of each side respectively, till you have gone round the field. To find the content. Rule Divide the field into triangles and trapeziums, and find the content of each part separately by the fifth and |