XXIV. 



BLTLE GLASS. 



IN May, 1871, General J. A. Pleasanton, of Phila- 

 delphia, gave before the Philadelphia Society 

 for the Promotion of Agriculture an account of some 

 experiments on " the influence of the blue ray of 

 sunlight and of the blue color of the sky in develop- 

 ing animal and vegetable life, in arresting disease, 

 and in restoring health in acute and chronic dis- 

 orders in human and domestic animals." 



These experiments began with the building of a 

 grapery in which every eighth row of glass in the 

 roof was colored blue. Only a part of the glass 

 was made of this color in order not to reduce the 

 temperature too greatly. The blue glass was so 

 placed, however, that all the plants in the house 

 would receive from it rays of blue light at some 

 time during the day. Vines placed in this house 

 grew the first year with wonderful rapidity, and 

 the second year produced an enormous crop of 

 fruit. 



Encouraged by this success General Pleasanton 

 next tried the effect of blue light on domestic ani- 

 mals. A piggery was built vrith blue glass in the 



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