SHADE TREES. 245 



tiou of our collector. It is not unlikely that the film of water on the bark 

 of trees during such periods would have a tendency to affect materially 

 the potential of the surrounding air, as Stahl has pointed out, and possibly 

 to equalize the electrical tension. The subject should have further investi- 

 gation, but we believe that it is possible to protect trees from injury by 

 lightning, whether they be atmospheric or earth discharges. 



Injuries to Trees from Arc Lamps. 



Damage to trees from artificial light rarely occurs. We know of only 

 one instance where any definite injury has occurred to trees from the use 

 of the arc light. Mr. William G. Keith, gas and electric light commis- 

 sioner of Cliicago, 111., has reported a case where the electric lights caused 

 damage to adjacent trees located on certain streets in Chicago. The 

 trees injured were in all cases young Carolina poplars. The particular 

 lamps causing the trouble were known as the G. E. Companj^, type W, 

 10 ampere, 465 watt, 1,000 candle-power, series flame arc lamps, and 

 were operated on the same circuits. These lamps were in operation nearly 

 a year. Shortly after their installation damage occurred to the poplars 

 adjacent to the lamps. The damage to the trees in all cases was confined 

 to that side near the source of light, the trees being stripped of leaves and 

 some of the branches apparently killed. The injury to the branches was 

 such that they became infested with borers. As the injury to the trees 

 seemed to be persistent where this type of lamp was employed and not 

 noticeable where other types of lamps were used, — such as the direct- 

 current open arc lamp and the 300-watt 600-candle-power gas-filled in- 

 candescent lamp, — the system was changed to the latter type, and the 

 trees became normal, throwing out new twigs and leaves. 



At fii'st it was thought that the heat generated by the lamps was re- 

 sponsible for the damage to the trees, but the heat generated from the 

 gas-filled lamps was equal to or greater than that from the other types; 

 hence it appeared that the damage did not result from the heat. Finally 

 it was demonstrated that the trouble was caused by the practice of empty- 

 ing the contents of the globes, consisting of such products of combustion 

 as fluorides and possibly other injurious salts which accumulate in them. 

 The trees were located very close to the lamps and somewhat below them; 

 hence in emptying the globes the poisonous products would fall on the 

 foliage. As already stated, the injury in all cases occurred on that por- 

 tion of the tree adjacent to the lamp, the other or remote portions being 

 unaff"ected. 



Tliis is apparently the first authentic case at least of noticeable injury 

 to street trees from electric lamps, and the theory of Commissioner Keith 

 relative to the specific cause of the injury to the foliage — namely, it 

 being due to the deposition of the products of combustion from the carbon 

 on the foliage — appears to be a most rational one. It should be pointed 

 out, however, that there are other ways in wliich injury of a similar 

 nature might occur to trees from electric lights, and as innovations in 



