Population  and  "Difeafes  of  Chefter.  133 
the  benefit  of  frefli  air  and  exercife,  without  incurring 
danger  from  catching  cold. 
The  walls  are  near  two  miles  in  circumference,  and 
furround  the  central  part  of  the  city : they  are  dry  and 
clean  immediately  after  the  heavieft  rains.  The  Rows 
form  a dry  communication  with  the  walls  from  nearly 
every  place  within  their  circuit:  their  frequent  afcents 
and  defcents;  their  elevated,  airy  fituation,  and  varied 
profpects ; all  contribute  to  render  walking  upon  them 
peculiarly  well  adapted  to  preferve  or  reftore  health. 
The  Dee,  a large  navigable  river,  divides  a fmall  part 
of  the  town  from  the  reft,  fkirts  the  lefs,  and  furrounds 
three  quarters  of  the  larger  portion.  Where  it  makes 
this  divifion,  it  falls  over  a caufeway,  forming  a widely 
extended  cafcade,  and  then  runs  with  rapidity  down  loofe 
rocks ; the  whole  defcent  is  thirteen  feet.  The  tide  al- 
ways flows  up  to  the  town,  where  it  rifes,  on  a medium 
of  fpring  tides  fifteen  feet,  the  higheft  tides  twenty-one 
feet : every  new  and  full  moon,  about  fix  or  eight  tides 
flow  over  the  caufeway,  and  fometimes  more  than  twenty 
miles  above  the  town.  Befides  wafhing  away  the  liquid 
filth,  which  quickly  runs  into  the  river  by  a fhort  courfe 
from  nearly  all  quarters  of  the  town,  the  agitation  of 
the  waters  both  by  the  cafcade  and  tides  is  probably  of 
farther  fervice  in  purifying  the  atmofphere. 
The 
