BOTANICAL  GARDENS   OF  THE  BRITISH  COLONIES.  327 
the  other  end,  another  glass  tube,  bent  at  right  angles,  clipped 
into  a  mercury  bath,  its  vertical  branch  being  80  centimetres 
long.    For  the  space  of  eight  or  ten  hours,  a  current  of  hydro- 
gen was  driven  through  the  apparatus,  which  was  maintained  at 
a  high  temperature,  so  as  to  exhaust  the  action  of  the  hydrogen 
on  the  sides  of  the  iron  tube,  and  to  drive  away  all  the  atmos- 
pheric air,  as  well  as  the  moisture  contained  in  the  tube,  or  likely 
to  be  produced  there.    This  done,  the  communication  between 
the  iron  tube  and  the  hydrogen  apparatus  was  cut  off  by  melting 
down  the  glass  tube  by  the  aid  of  the  blowpipe.    No  sooner  was 
this  effected,  than  the  mercury,  no  longer  kept  down  by  the 
stream  of  hydrogen,  yielded  to  the  pressure  of  the  air,  and  rose' 
in  the  vertical  glass  tube  to  the  height  of  740  millimetres,  or 
very  nearly  the  usual  barometrical  height.   This  would  not  have 
happened,  had  there  not  beeri  a  nearly  complete  vacuum  in  the 
tube  the  instant  the  supply  of  hydrogen  was  cut  off.    But  what 
had  become  of  the  hydrogen  supplied  before  ?   There  is  but  one 
explanation  possible,  viz  :  that,  notwithstanding  the  pressure  of 
the  atmosphere,  the  hydrogen  had  passed  through  the  pores  of 
the  steel  tube.    Hence  an  iron  tube  introduced  into  a  furnace 
where  there  are  reducing  gases,  is  a  most  powerful  instrument 
for  carrying  off  all  the  hydrogen. — Amer.  Journ.  Sci.  and  Arts, 
May,  1864,  from  Galignani. 
BOTANICAL  GABDENS  OF  THE  BEITISH  COLONIES. 
One  of  the  principal  supports  for  the  cultivation  of  the  Natu- 
ral Sciences,  and  which  insure  her  superiority,  England  derives 
from  the  numerous  botanical  gardens,  which  have  been  established, 
some  of  them  for  a  considerable  time,  and  all  of  them  under  the 
supervision  of  competent  men,  at  various  stations  in  her  principal 
colonies.    Among  these : 
In  Canada,  the  Kingston  Botanical  Garden,  Dr.  Lawson,  Di- 
rector. 
In  Jamaica,  the  Bath  Botanical  Garden,  N.  Wilson,  Super  - 
intendent. 
In  Trinidad,  St.  Anne's  Botanical  Garden,  Dr.  II.  Kreuger, 
Director. 
