28 



Table XI showing loss of light in some typical Massachusetts 

 greenhouses running east and west. Outside light conditions in 

 open air equals 100%. 



All glass 16 X 24 in., but in No. 4 the glass was placed, length- 

 wise; that is, the rafters were 24 inches apart. 



The data given here were obtained from large, modern rose 

 houses running east and west. The tests were all made in the 

 winter, in bright sunshine, when snow was on the ground, and are 

 averages of two experiments, running from 8 a. m.. to 4 p. m. in 

 one case, and from 1.30 to 4 p. m. in another. The readings were 

 in all cases taken 5 feet from the roof glass, a favorable location 

 for obtaining average results. The houses ranged from 20 to 40 

 feet wide, and 300 to 700 feet long, and some were built of wood, 

 others of iron. All had about the same roof angle. No. 4, an 

 iron house, had iron rafters 4 inches wide. None of the houses 

 was over 15 years old, and all were in excellent condition in every 

 respect. Houses Nos. 1 and 4 were newer than Nos. 2 and 3, 

 but the heavy iron rafters in No. 4 cast a greater shadow. Very 

 little difference was shown in the percentage of light lost in these 

 houses, where the period of exposure occupied nearly the whole 

 day. Other records taken at shorter intervals during the forenoon, 

 as well as in the afternoon, showed greater differences in the light 

 records of the houses. In all cases No. 4, which was the newest 

 house and had 16 x 24 glass, lengthwise, gave the best results. 

 No. 1, which was not a very old house, gave the next best, and 

 Nos. 2 and 3, slightly older, made of wood and glazed with older 

 glass, did not show up so well in the morning and afternoon re- 

 cords for short periods. The large iron rafters in No. 4 cast heavy 

 shadows, and this is probably one of the reasons why the light 

 conditions in this house did not show up better. All these houses 

 are located in the country where they were not subject to dust and 

 smoke. The loss shown even by the older houses, namely 22 per- 

 cent, is small as compared with other houses not so favorably 

 located or so well constructed. 



The following table shows tests made in houses of different 

 ages and types of constniction, running north and south. All the 

 readings were made five feet from the glass. 



