29.  Owing  to  the  earth  accomplishing  a  complete  revolu-
tion upon  its  axis  in  twenty-four  hours,  |;he  sun  appears  to
perform  a  circuit  round  it  in  that  space  of  time ;  and  as  360°
are  thus  described  in  twenty-four  hours,  15°  are  passed
through  in  one  hour,  and  1°  in  four  minutes.  Hence  places
differing  in  their  longitude  1°,  15°,  or  30°,  and  so  on,  differ  in
their  time  four  minutes;  one  hour,  and  two  hours ;  and  if  we
know  the  difference  of  time  between  any  two  places,  we  can
estimate  their  difference  in  longitude.  As  the  earth  revolves
from  west  to  east,  places  to  the  eastward  of  us  receive  the
light  of  the  sun,  and  lose  it  sooner  than  we  do,  that  is,  have

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irSI  Ol*  HAPS  AlTD  OLOBIS.  11

Bcmiifle,  noon,  and  suiiBet  sooner;  and  places  to  the  westward
of  ns  haye  sunriBe,  noon,  and  sunset  later.  Thus,  if  a  good
chronometer,  taken  out  bj  the  seaman  from  Gbeenwiohy
points  to  12  o'clock,  or  noon,  when  he  arrives  at  New  Toi^
while  the  time  at  that  place  is  7h.  4m.  in  the  early  mominff,
the  difference  is  4h.  56m.,  equal  to  74^  of  longitude,  whidi
must  be  west  of  Ghreenwich,  as  the  New  York  time  is  later.
The  eastern  and  western  limits  of  the  United  Kingdom  are
12^  apart  in  longitude,  equal  to  a  difference  of  48  minutes
of  time ;  and  hj  that  space  the  fishermen  of  Suffolk  hail  the
sunbeams  before  thej  are  caught  bj  the  inhabitants  of  Ire>
land's  western  isles.
