13 



Table II showing the difference between morning and afternoon 

 light in a bell jar. Exposures from 9 a. m. — 12 m. and 12 m. — 3 p. m. 



These experiments were made for a special purpose, and 

 as far as they went (six months) covered the same period as those 

 shown in Table I. The same general difference in the morning 

 and afternoon light conditions is seen here. The percentages are 

 not so high as those in Table I, although the average for the six 

 months is the same as that for one year in the preceding series. 

 The monthly averages in all cases, however, are higher than those 

 in Table I, a fact due in part to the concentration of the light rays 

 in the bell-glass on the recording tube, and also to the absence of 

 shadow. The following summary table gives the results of all the 

 experiments, together with corresponding outdoor records. 



Summary table III showing comparison of light records for 

 corresponding periods during the day, obtained from bell jar, from 

 greenhouse and outside of greenhouse. Records of exposure from 

 9 a.m. — 12 m. and 12 m. — 3 p. m. in all cases except in experiment 

 field, where they were made from sunrise to noon, and from noon 

 to simset. 



A comparison of the results given in the summary table shows 

 an average difference of 10 percent, in the morning and afternoon 



