25 



Applying this rule we must say that, so far, it would take a con- 

 siderable stretch of the imagination to discover any difference in 

 the plants which could be attributed to lack of light caused by 

 distance from the glass. But we have also used another method. 

 It consists briefly in the detennination of the varying intensity of 

 light by a chemical method, and we have been assured that it is 

 extremely sensitive and absolutely accvirate. Carefully applying 

 this test we have been able to find no dift'erence between light 5 

 feet from the glass and 25 feet. There may be a point at which 

 some difference will be found, but someone will have to seek for it 

 in a house considerably wider than 40 feet. 



If the time ever comes when, in place of the whims and fancies 

 of weak and mortal m.an, we have exact scientific methods for solv- 

 ing the complex problem.s of the adaptability of glass structures to 

 plant growth, then and not until then, will the perfect greenhouse 

 be produced." 



The many tests which we have made are identical with Mr. 

 jMontgomery's, who used our apparatus. We found that there 

 was no perceptible difference in the light intensity in different parts 

 of greenhouses except that caused by shadows, dirty glass, etc. 

 In some of our tests, which lasted practically a whole day, we re- 

 corded the conditions of the light at distances varying from 5 feet 

 to as great a distance as we were able to obtain in houses 40 feet 

 wide, with precisely the same results. Greenhouse glass has a 

 more or less tuieven surface, besides being somewhat concave, and 

 for this reason the light waves as they pass through are more or less 

 deflected. The maximum effect of such deflections, however, is to 

 be seen close to the glass; and as one gets farther away from the 

 glass a more or less uniform diffusion is secured. In fact, the 

 farther away the plants are from, the glass the better, for at a dis- 

 tance they obtain a more uniformly diffused light which renders 

 them less liable to injury from concentrated rays through irregu- 

 larities, glass bubbles, etc. In m,any instances we obtained larger 

 readings from our tubes exposed, directly under the glass than else- 

 where, the irregular glass acting as a lens and concentrating the 

 rays. Even the small shadows in a greenhouse diminish and are 

 lost sight of at certain distances from, the glass, therefore produce 

 no visible or local effect on the plant, although the shadows cast 

 by opaque objects do affect the light intensity as a whole. Un- 

 even surfaces and bubbles, characteristic of greenhouse glass, must 

 be regarded as a drawback, since an even, smooth glass will trans- 

 mit light more uniformly and im.prove the light conditions; con- 

 sequently some im,provemcnt in greenhouse lighting may be had 

 by using better glass. 



As regards draughts, etc. in the large houses, these will be found 

 in all houses whether large or small, and it is apparent that the 

 best system of ventilation has not been worked out as yet either 



