104 MODERN SCIENCE READER 



world's creation which according to some theorists formed 

 the atmosphere, and has since kept the oxygen present in 

 it a practically constant quantity. 



It must be borne in mind, however, that, although such 

 an equation is capable of representing the sum of the 

 actions taking place, yet it only in reality represents the 

 first and final stages of a series of most wonderful and 

 beautiful reactions, the exact course of which is but little 

 understood. The fact that the sun's energy is necessary 

 to bring about this reaction is made manifest by the growth 

 of vegetation when kept from the light, when it merely 

 gives rise to a few sickly and colorless shoots formed by the 

 plant food already stored in the plant or seed, while on the 

 other hand recent experiments have shown that ordinary 

 vegetation can be accelerated in its growth by the illumina- 

 tion from certain forms of artificial light during the hours 

 of darkness. 



Probably the first attempt to use artificial light for 

 hastening the growth of plants was made in 1861 by Herve- 

 Magnon, while twenty years later Siemens, by experiment- 

 ing with an arc lamp of 1,400 candle power, placed ten feet 

 from the plants, with a glass screen interposed, came to the 

 conclusion that this illumination was capable of producing 

 an effect equal to about half that of the sun. In more 

 recent years various artificial lights have been employed 

 for accelerating growth, and it has been found that nearly 

 all plants, aided in their development by artificial light to 

 which they are exposed during the usual hours of darkness, 

 reached the flower and fruit bearing stage much earlier 

 than with sunlight alone, some few, however, like the onion, 

 declining to be hurried. That this growth and progress is 

 not at the expense of root formation is abundantly proved 

 in the case of such plants as radishes, in which not only was 

 the top growth three times that of a similar plant growth 

 in sunlight alone, but the root growth also amounted to 

 two and a half times the normal in a given time. 



From the exhaustive researches which have been made 



