31 



inch No. 2 glass, while the former, of Lord & Burnham iron con- 

 struction, is glazed with 24 x 24 inch glass on the roof, and on the 

 sides with 16 x 24; i.e., 16 inches between sash bars, hence the 

 light conditions in one house are slightly better than those in the 

 other. 



The least loss of light is given by the entomological conserva- 

 tory. This house is a Weathered construction, with curvilinear 

 roof, and is well lighted. The glass, however, is 16 x 24 inches and 

 of the same quality as that in the other houses. Its excellent light 

 may be partly due to reflection from, the partition wall, which we 

 could not very well avoid. The curvilinear construction of the 

 house, however, undoubtedly adds much to the light. 



The Experiment Station vegetation house, built twelve years 

 ago, runs north and south and has sides 7 feet or more high. The 

 Experiment Station south house runs east and west. It is about 

 12 X 40 feet and is 14 or 15 years old. The Durfee lower house is 

 nearly square, the roof slanting towards the south and also towards 

 the east. The sides are 7 or 8 feet high, and. both roof and sides 

 are glazed with 16 x 24 inch glass. This house was remodelled 

 about 18 years ago. The upper house is about the sam.e age, and 

 this and the preceding one, have low angle roofs. 



In all cases our tests were made the same distance from the 

 glass in the roof and sides, except in the north and south houses, 

 where the readings were taken at some distance from the glass. 

 These 2 or 3 hour tests show the effects of the age of the glass, al- 

 though they are fairly typical so far as the relative light conditions 

 are concerned, in all cases being based on the outdoor readings. 

 In the preceding tables we have given the loss of light in green- 

 houses based on outdoor observations for brief periods, and in the 

 following table they are given for more prolonged periods. 



The records in the following table, which show average monthly 

 light conditions, will convey some idea of the light in greenhouses 

 as compared with that out of doors for a whole year. The tests 

 lasted only three hours in the morning and three in the afternoon, 

 or from 9 a. m. — 12 m., and 12 m. — 3 p. m., the location of the 

 greenhouse preventing longer periods of exposure. The green- 

 house was 12 x 40 feet, having an even span roof glazed with No. 

 2, 16 X 24 inch, double thick glass. The direction was east and 

 west, or to be more accurate, about 25° north of east, and the 

 recording tube was placed, 5 feet from the glass and 5 feet from the 

 south wall. The glass in the roof had been in use for about 8 

 years, and that on the sides about 10 years longer. The wood 

 framework was not as light as it might have been, but the exposed 

 tube was placed where it could receive direct sunlight through the 

 roof. 



