INTRODUCTION. XXlll 



SO highly charged with noxious matters, that many 

 deciduous plants, and almost all evergreens, cease to 

 flourish, or exhibit only a sickly vegetation. In an 

 interesting biographical sketch of his late lamented 

 friend Dr. Turner, Professor Christison confirms, by 

 subsequent experience, the opinion formerly given 

 respecting the noxious operation of the sulphurous 

 and muriatic acid gases on plants ; he describes their 

 action as so energetic, that, in the course of two days, 

 the whole vegetation of various species of plants may 

 be destroyed by quantities so minute as to be alto- 

 gether inappreciable by the senses. On two occa- 

 sions he was able to trace the identical effects of the 

 same kind of works (the black ash manufactory) on 

 the great scale which his friend and himself witnessed 

 in their researches. In one instance, the devastation 

 committed was enormous, vegetation being for the 

 most part miserably stunted, or blasted altogether, 

 to a distance of fully a third of a mile from the works, 

 in the prevailing direction of the wind." 



Mr. Elhs's is an extremely pleasing and well-written 

 paper ; it is full of very valuable information, collected 

 with industry, and arranged with care ; the experi- 

 ments to which he refers are of undoubted autho- 

 rity, and strictly applicable to general principles in 

 the way intended by their various authors. I think 

 they will be received as conclusive by that large class 

 of readers which prefers the dictum of a philosopher 

 to the fatigue of inquiry ; but never by that limited 

 class — that troublesome and inquiring class — which 



