20 



placed from the horizontal at angles of 10, 30, 60 and 90 degrees, 

 the 90° glass of course being vertical. The differences shown are 

 those between each angle, the difference in the absorption of light 

 at 90° and at 10° being 29 percent. The glass placed at 60° was 

 nearly as well situated for absorbing rays at this season of the year 

 as the one at 90°, there being but 5 percent, difference between the 

 two, and 24 percent, difference between any 60° and 10° glass. 



From the results of these experiments it is quite evident that 

 there is much loss of light from reflection, and some growers of 

 special crops have attempted to overcome this loss by constructing 

 roofs with greater angles. 



REFLECTION OF LIGHT FROM DIFFERENT SURFACES. 



As niight be expected, there is considerable difference in the 

 amoiint of light reflected from different surfaces. White is the 

 princi])al color used on the outside and inside of greenhouses, 

 either lead paint or whitewash being used, but most of the iron 

 work is dark in color. Some tests were made of aluminium bronze, 

 white and dull Ijlack paints, the colors used in our own greenhouse, 

 to determine their value as reflectors of light. In our experim.ents 

 we used both metal and boards painted with the above named sub- 

 stances, and in some experiments not given here we tested various 

 other surfaces. The tests were arranged in such a way that the 

 direct sunlight was excluded, although the recording tubes were 

 vmdou1)tcdly affected to some extent by diffused light. This, how- 

 ever, was the sam.e in each test and can therefore be eliminated in 

 our comparative tests. The tests were made in bright sunlight 

 out of doors. The tubes were arranged in such a way that they 

 would receive the full benefit of the reflected rays. 



The results of these experiments follow. 



Table VI showing the amount of light reflected from different 

 surfaces. Average of three experiments. 



It will be observed from the table — an average of three ex- 

 perim.ents with m.etal backgrotmds — that the aluminium bronze 

 reflected the largest percentage of light, followed In- white paint 

 and by dull black paint. The white paint reflected 12 percent, less 



