I 



17 



1-S inch thick, with rather fine flutinj:;s and a fjeneral ai^jwarance 

 of opaque ^lass. The No. 2 French, double thick, is used exten- 

 si\'ely in j^recnhouse construction in the east, and the No. 3 

 American in other sections of the country. The fluted glass is 

 not used for greenhouses, although it is valuable for dispersing light. 



The diflference in the quality of the glass tested was suflficient 

 to enable one, with no previous knowledge of how they were placed, 

 to pick out each sample at a distance of six rods. The results of 

 the tests given in the table show that the differences in the quality 

 or light transmitting properties of the glass are marked. The No. 2 

 gave 17 i^er cent, less light than No. 1 , and No. 3, 32 ^x^r cent, less than 

 No. 1, while the fiuted glass was practically as good as No. 3, al- 

 though from, its opaque appearance it could hardly be thought to 

 compare with any of the others. The relatively high records 

 given by this glass are explained by the fact that the fiutings act 

 as lenses, and it is evident that the rays of light in our experimxnts 

 were concentrated upon the recording tubes, which were only 

 about 2 1-2 inches from the glass, and the readings obtained from 

 this glass are probably somewhat misleading. 



The cost of the different qualities of glass at the time of pur- 

 chase was as follows: No. 1, 42c; No. 2, 39c; No. 3, 33c; the 

 fluted, 20c per light. Considering the results obtained from the 

 different types of glass. No. 2 would seem a wiser purchase than 

 No. 3. Large dealers say that they sell nine boxes of French glass 

 to one of American in the east for greenhouse use. According to 

 this schedule of prices, those who purchase No. 2 glass pay six 

 cents more or 15 per cent, more than those who buy No. 3, but 

 receive 18 i^er cent, more light. We believe that it would pay to 

 use No. 1 quality in some special cases. 



Since most plants receive far below the optimum light in the 

 winter months in our latitude, the choice of glass should have care- 

 ful consideration. In the spring and sum.m,er this is less important, 

 and in many cases it is even of advantage to shade the plants at 

 this tim.e. However, the am.ount of light is not dependent wholly 

 on the quality of glass, as the size of the house and methods of 

 construction are important features, and will be discussed else- 

 where. 



Table IV showing results obtained from different kinds and 

 qualities of glass. 



1 1 Percentage of de- 



Readings, 'creased light value. 



Lst quulity glass, 



2d quality glass, 



3rd quality glass, 



Fluted glass, 



