19 



THE EFFECTS OF DIFFERENT ANGLES OF GLASS ON THE 

 LIGHT m GREENHOUSES. 



It is well known that light vi"ill penetra: a :rinsparent object 

 more easily when the object is placed at r:^-:.-. ar.gles to the ra^-s 

 oi light. Although greenhouse constructors and n^anagers realize 

 this, for many reasons most greenhouse roofs are built at different 

 angles regardless of the loss of light resulting from reflection. 

 Moreover, the sun not only strikes the house at different angles 

 during the day, but at different seasons of the year, so that there 

 is a great deal of variation in the light reflection. But the houses 

 with greater roof angles, in which there is less reflection, allow more 

 light to pass through, and of course there would be a gain in light 

 transmission by utilizing angles which would give the maximum 

 average effect in certain seasons. For instance, a house having an 

 angle of 60° will transmit more light than one with a 20° angle. 



A few obser\'ations on the amount of light lost by reflection 

 were made with glass placed at different angles. In two houses 

 running east and west, with roof angles of 32" and -46° respectively, 

 tubes were exposed from S a. m. to 4 p. m. with the following re- 

 sults: 



House with roof angle of 32° gave a reading of ^5. 

 " " •' "_46° " " ^ " " 545. 



Diilerence. IS^f. 



These observations were made February* S, when the sun was 

 not ver\- high. The roof with an angle of 46° was much better 

 adapted to allow the light to pass through the glass at that time of 

 the year than the other house. Another experiment was conduct- 

 ed in which glass of differeti^*qualit\- was placed at different angles 

 with the following results : 



Table V showing the amount of light transmittec at different 

 angles. Duration of experiment — ^3 hours 



Angles of Relative percentage T^ae of differ- 



Gliiss. Readings- entangles. 90°— 100%. 



9orc 



71% 



These results are an average of three experiments made in the 

 third week of January, when the sun was not ver\- high. In each 

 case exposures were made from 9 a. m. to 12 m. The glass was 



