724 



PRACTICAL DIAGRAMS. 



Fig. 1039. Fig. 1040. 



ground. They are from a German work 

 entitled " Handbibliotheck fur Gartner," 

 by Ligilir of Berlin. 



Rules for calculating the length of sha- 

 dows. — In selecting situations for gardens, 

 and also for planting trees for shelter, the 

 length to which their shadows will reach 

 during winter deserves consideration, as 

 also does that of the shade caused by 

 walls and other buildings ; for no screen 

 should be planted so close as to shade 

 any part of the ground, nor any glass 

 roof be erected on which the sun may 

 not shine every day in the year. 



Several rules are given for determining 

 this. The relation between the height of 

 a tree and the length of its shadow de- 

 pends on the latitude of the place and 

 the sun's declination, which latter will be 

 found by consulting an almanack, and 

 the former by the sun-dial— at least, most 

 sun-dials have the latitude engraved on 

 them ; if not, the map of the county will 

 give it. The height of the tree, wall, or 

 building, and the length of its shadow on 

 the ground, form the perpendicular and 

 base of a right-angled triangle, the hypo- 

 thenuse of which angle is represented by 

 that of the sun's rays from the top of the 

 tree to the ground. This hypothenuse, 

 or direction of the sun's rays at noon, 

 always forms, with the ground line, an 

 angle equal to the amount of the latitude 

 and the sun's declination added together, 



from the 20th of March till the 22d of 

 September; but, from the 22d of Sep- 

 tember till the 20th of March, the sun's 

 declination is to be subtracted from the 

 amount of the latitude. This angle being 

 found, and the height of the wall, house, 

 or tree taken, all the rest will be found 

 by the rules of trigonometry. 



The following simple rule may be of 

 use to such as do not understand geo- 

 metry or trigonometry, and will give the 

 shadow near enough for practical pur- 

 poses : — 



Multiply the height of the wall, tree, or build- 

 ing— 



In latitude 51 | c 

 52° 



53° 

 54° 

 55° 

 56° 

 57° 

 58° 



The product will give the length of the shadow 

 at noon on the shortest day. 



Ex.am.ple. — What will be the length of the 

 shadow of a tree 10 feet high, in latitude 52° on 

 the shortest day? 



3.852 the multiplier for latitude 52°. 

 10 the height of the tree. 



by 3.719. 



~ 3.852. 



„ 4.149. 



„ 4.402. 



„ 4.895. 



„ 5.369. 



„ 5.944. 



_ 6.651. 



38.520 

 12 



6.240 

 12 



2.880 Ans. 38 feet, 6 inches, 2 parts. 



