32 



Table XIV showing difference in light inside and outside of 

 greenhouse for a period of one year. Records taken daily from 9 

 a. m. to 3 p. m. 



The percentage of light lost under glass is shown in the monthly 

 averages given in table XIV, which gave an average throughout 

 the year of 22 percent. The largest loss occurred in the month of 

 December, which was 43 percent., followed by January, 34 per- 

 cent., and March, 26 percent.; in other words, those m^onths which 

 have the shortest days when the sun is lower in the heavens and 

 when there is more frost, snow and condensed moisture on the roof, 

 show the greatest difference. On the other hand, the least differ- 

 ence is shown in June and July, when the sun is highest and when 

 the light rays strike the glass at more favorable angles. Part of 

 the difference m.ay be due to the reflection of the light from the 

 snow on our recording apparatus, for this reflection would be pro- 

 portionately greater on the outside exposed tube than on the one 

 exposed inside. 



Comparing the average monthly outside records for the whole 

 year it was found, as m.ight be expected, that there is much better 

 light in the summer than in Decem,ber or January. Neither this 

 ratio nor that between the outside and greenhouse conditions, as 

 shown in the table, is accurate, for the decomposition and conse- 

 quent loss of efficiency of the chemical substances used to record 

 the light take place m.ore rapidly in intense light. Therefore the 

 actual light of January and June is different from that shown in 

 the table; also the differences between the light out of doors and 

 that under glass are slightly greater than those shown in the tables 

 for any period. These experiments do not show the relative value 

 of east and west and north and south houses from the light stand- 

 point, and to do this would retjuire different conditions. The 

 longest days, with the most intense light, come in June, and it 



