2 J 
Literature , &c, with Commerce . 
completely demonftrated the method by which 
Nature makes ufe of the leaves of vegetables to 
purify the atmofphere, when contaminated with 
putrid or pldogiftic vapours. When in this Itate, 
every leaf ads as a flrainer to the air, imbibing 
and applying to the nurture of the plant, fuch 
parts as are unfit for animal refpiration, and 
throwing it out, thus filtered and fuited to ad 
again as a menftruum for the phlogifton, which 
is continually evolving by the breathing of ani¬ 
mals, the corruption of vegetables, and by the 
many various proceffes which are by nature and 
by art continually carrying on. 
Eledricity is another branch of fcience which 
has afforded great light to the operations of 
nature. A knowledge of its leading principles, 
and a dexterity in making a number of entertain¬ 
ing experiments, may be attained by moderate 
application, and thereby, a field of amufement 
opened to the mind, at an eafy expence of time 
and money. 
To obtain a perfed acquaintance with the 
fcience of Optics, much attention and clofe ap¬ 
plication would be requifite. Such a knowledge 
of it, however, as is l'ufficient for general pur- 
pofes, is eafily arrived at. The nature of the 
refledion and refradion of the rays of light, of 
vifion, and of colours, the properties of lenfes, 
are ufeful and entertaining objeds of inquiry. But 
the very minute divifibility of the rays of light 
C 3 fills 
