200 



THE GAKDENER'S ASSISTANT. 



Before proceeding further in this subject, it 

 will be necessary to refer to fig. 260, in which 

 the lines ab c comprise a quadrant or quarter of 

 a circle, the arc of which, a b, is supposed to be 



Tig. 260. 



divided into 90 equal parts or degrees. Then, 

 if c b represents the width of a house and b d 

 the back wall, c d, the roof, will have an eleva- 

 tion of 30°. When the angle of elevation is 45°, 

 it will be observed that the width of the house 

 and the height of the back wall are equal, that 

 the line of roof c e cuts through half the quad- 



rant, and that the angles at c and e are equal; 

 but this is not the case with any other slope of 

 roof whatever. Many gardeners designate the 

 slope, not according to the angle which it makes 

 with the base, but with the back wall; whether 

 it is the one or the other should be distinctly 

 indicated, otherwise serious errors might be the 

 consequence. Thus the angle c b d might be 

 designated, counting from the back wall, an 

 angle of 60°; and if this circumstance were not 

 mentioned, a house with a roof sloping 60° from 

 the base might be constructed, when in reality 

 an angle of 30° with the base is meant. 



As the slope of the roof is dependent on the 

 relative dimensions of the house, and vice versd, 

 the following table, which has been constructed 

 to show by inspection the angle of elevation 

 rendered necessary by various dimensions, will 

 perhaps prove useful. To use it, look for the 

 width of the house, say 15 feet, in the left-hand 

 column, and at top for the number of feet by 

 which the back wall exceeds the front wall in 

 height, say 12, and where the two columns 

 intersect will be found 38° 40', the angle of 

 elevation corresponding with that width of 

 house and height of back wall above the front, 

 that is, above the eaves. 



Width of 









Hciyht of Back Wat 



I above Front Wall in Feet. 



House in 

 Feet. 













j 



< 



I 



3 



4 





5 



i 



6 



7 



8 



9 



10 



11 



12 



13 14 



15 



5 



21° 



48 



30° 58' 



38 e 



39' 



45' 



0' 50 a 



12' 



54° 27' 



58° 



0' 



60° 57' 



63° 26' 



65° 34' 



67° 3' 



68° 58' 



71° 21' 



71° 34' 



6 



18 



26 



26 33 



33 



41 



39 



48 



45 







49 24 



53 



8 



56 18 



59 2 



61 24 



63 27 



65 13 



m 48 



68 12 



7 



15 



56 



23 12 



29 



44 



35 



32 



40 



36 



45 



48 



49 



52 7 



55 



57 32 



59 45 



61 42 



63 26 



65 



8 



14 



2 



20 33 



26 



33 



32 



<> 



36 



52 



41 11 



45 







48 22 



51 20 



53 58 



56 19 



58 24 



60 16 



61 56 



9 



12 



31 



18 26 



23 



57 



29 



3 



33 



5 



37 52 



41 



38 



45 0- 



48 



50 43 



53 8 



55 18 



57 16 



59 2 



10 



11 



19 



16 42 



•21 



48 



26 



36 



30 



58 



35 



38 



39 



41 59 



45 



47 44 



50 12 



52 26 



54 27 



56 19 



11 



10 



18 



15 15 



20 







24 



26 



28 



36 



32 28 



36 



2 



39 17 



42 16 



45 



46 50 



49 46 



51 51 



53 45 



12 



9 



27 



14 2 



18 



4 



22 



57 



26 



33 



30 15 



33 



41 



36 52 



39 48 



43 10 



45 



47 57 



49 24 



51 20 



13 



8 



44 



13 



17 



6 



21 



2 



24 



47 



28 18 



31 



36 



34 42 



37 34 



40 14 



42 3 



45 



47 7 



49 5 



14 



8 



8 



12 5 



15 



56 



19 



39 



23 



12 



26 34 



29 



44 



32 44 



35 39 



38 9 



40 36 



42 53 



45 



47 



15 



7 



35 



11 17 



14 



55 



18 



26 



21 



48 



25 1 



28 



4 



30 58 



33 41 



36 15 



38 40 



40 55 



43 



45 



16 



7 



7 



10 37 



14 



2 



17 



21 



20 



33 



23 38 



26 



33 



29 21 



32 



34 



36 52 



39 5 



41 11 



43 9 



17 



6 



42 



10 



13 



14 



16 



24 



19 



26 



22 21 



25 



12 



27 54 



30 28 



32 54 



35 13 



37 24 



39 28 



41 25 



18 



6 



20 



9 27 



12 



31 



15 



31 



18 



26 



21 15 



23 



57 



26 34 



29 3 



31 26 



33 5 



35 50 



37 52 



39 48 



19 



6 







8 58 



11 



53 



14 



44 



17 



31 



20 14 



22 



50 



25 21 



27 46 



30 4 



32 16 



34 23 



36 23 



38 17 



20 







42 



8 31 



11 



19 



14 



2 



16 



42 



19 17 



21 



48 



24 14 



26 36 



28 49 



30 58 



33 



35 



36 51 



The question now is, What are the best angles 

 to adopt for the roofs of houses intended for 

 forcing fruits so as to ripen them at different 

 seasons, and for the growth of plants? It is 

 well known that when the sun's rays fall upon 

 glass in a perpendicular direction or nearly so, 

 very few rays are reflected ; but when they meet 

 the surface of the glass in a very oblique or 

 slanting direction, more rays are reflected than 

 pass through it. According to Bouguer's table 

 of the rays reflected from glass, of 1000, when 

 the angle of incidence is 



1°, 25 



rays 



are reflected. 



50°, 



57 



rays 



are reflected 



10, 25 







60, 



112 







20, 25 







70, 



222 





»j 



30, 27 







80, 



412 





jj 



40, 34 





,, 



85, 



543 





5J 



From this it will be perceived, that at angles 

 of incidence from 1° to 30° the number of re- 

 flected rays is nearly the same, therefore the 

 roof of a house may have as much as 30° higher 

 pitch than that on which the sun's rays would 

 fall perpendicularly, without any important 

 diminution in the light transmitted to the in- 

 terior. It is certain that any plane of glass, 



