h st 4 
cautions to be obferved,. which I 
extracted from the are Ny of 
the-author. 
He reduces; the various fources 
from which errors may arife in this 
manner of. exploring air to twenty; 
which are, however, not all of equal 
importance, and may counterbalance 
in fome meafure ‘one another,’ fo 
that one error>may correct another. 
‘But fome of thefe are of fuch im- 
portance, that by Ned Seagate 8 them 
it may happen t na the itmo- 
{pheric air fhall appear: 
poifonous one. 
Thofe errors may originate prin- 
| cipally . either from the great tube 
er. meafure, or from the liste mea- 
fare. oe 
The. chic which may originate 
from: the fmall meafure are feven + 
