12 



In these experiments we studied the difference in inorning and 

 afternoon light in the greenhouse and out of doors from 9 a. m. to 

 12 m. and from 12 m. to 3 p. m. ; also the differences between out of 

 door light conditions and those in a bell-glass for the same periods 

 of time; and again, the difference from siinrise to noon and from 

 noon to sunset. The observations in the last two series were 

 made for only six months. 



Table I, showing difference between morning and afternoon 

 light in the greenhouse. Exposures from 9 a. m. to 12 m., and 

 12 m. — 3 p. m. 



The experiments shown in table I, which lasted one year with 

 practically no interruption, were made in a greenhouse 12 x 40 

 feet, running east and west. This was an even span house with 

 the usual roof slope, (30°) and was about IS years old. Eight 

 years before these records were made it had been remodelled and 

 glazed with new No. 2, double thick greenhouse glass, 16 x 24 

 inches. (See page 16). The sides had the original glass, about 

 12 X 22 inches. The light records were taken from 9 a. m. to 12 m. 

 and from 12 m. to 3 p. m. at a point about 4 feet from the roof 

 and 5 feet from the south end of the house, and in all cases showed 

 a greater percentage of light for the morning than the afternoon; 

 the average for the year, based on monthly averages, being 10 

 percent in favor of the morning light. The greatest difference 

 is shown in November and December, where the percentage 

 (daily average) is 20 and 27 percent respectively; while the small- 

 est difference (only .9 percent) is shown in January. Records 

 were also taken for a period of six months under a bell-glass, 12 x 20 

 inches, which extended through the roof of the greenhou.se. The 

 data are given in the following table. 



