544 



SCIENCE OF AGRICULTURE. 



Part 1 1. 



require to be taken, 

 objects. {Jig. 525.) 



to show particular trees, buildings, the depth of water, or other 



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3350. With respect to the elevations and shapes of hills and mountains, they are only t 

 be iieasured correctly by the quadrant and theodolite in the hands of regular land- 

 surveyors. Their shape and dimensions are laid down in maps in the same manner 

 as those of smaller deviations from the flat surface. Inaccessible dimensions of height, 

 as of trees or buildings, are obtained by the quadrant, or by relative comparisons of 

 shadows ; of depth, as of water or wells, by rods ; of breadth or length, by finding the 

 two angles of a triangle whose base shall be in one extremity of the distance, and apex 

 in the other. These, and many other equally simple problems in trigonometry, need not 

 be enlarged on, because they must be supposed to form a part of general education. 



3351. In portraying the general surface of land estates, different modes have been 

 adopted by modern land-surveyors. The first we shall mention is the old mode of giving 

 what may be called the ground-lines only ; as of roads, fences, water-courses, situations 

 of buildings and trees, {fig. 526.) This mode has no other pretension than that of 

 accuracy of dimensions, and can give few ideas to. a stranger who has not seen the pro- 

 perty, beside those of its contents and general outline. 



526 527 



r- 



3S52. In the second, elevations of the objects are added to these lines ; but which, m 

 crowded parts, tend much to obscure them. {fig. 527.) This mode is perhaps the best 

 calculated of any to give common observers a general notion of an estate ; more especially 

 if ably executed. Very frequently, however, this mode is attem.pted by artists ignorant 

 of the first principles of drawing, optics, or perspective, and without taste. The Ger- 

 mans who, in general, are far better topographical draughtsmen than any other people, 

 excel in this manner, and contrive, by joining to it Lehman's mode of shading the sur- 

 face, to produce pictorial plans of extraordinary accuracy and beauty. The most 

 perfect artist in this style who has ever appeared in England is Mr. Hornor, whose 

 work on the subject will be afterwards referred to. Were landed proprietors aware 

 that their estates could be mapped in this manner almost as cheaply as by the ordinary 

 mode, they would not rest satisfied with the meagre delineations generally made out. 



3353. In the third, a vertical profile, or geometrical birdseye view, that is, a birds- 

 eye view in which all the objects are laid down to a scale, is presented. In this the upper 

 surface of every object is seen exactly as it would appear to an eye considerably elevated 

 above it, and looking centrally down on it. {fig. 528.) This mode, properly executed, 

 is calculated to give a more accurate idea of the furniture or surface-objects of an estate 

 than any other ; and if the declivities be correctly indicated, and the shade of the hollows 

 and eminences be laid on with reference to some medium elevation, referred to or 

 illustrated by sections taken in the direction of indicated lines (a b), it will give an 

 equally correct idea of the variations of the ground. In short, it is the best mode for 

 most purposes, and is now coming into general use. 



