380  Royal  Society : — 
tion  be  repeated,  another  arc  A  B2  will  be  found  (whose  radius  is 
four  times  A  O)  equal  in  length  to  A  B.  This  construction  can  be 
repeated  indefinitely,  and  thus  a  portion  of  A  T  is  determined  equal 
to  A  B  ;  this  is  what  Mr.  Harris  calls  the  process  of  unbending  an 
arc.  Now  the  only  remark  we  have  to  make  on  this  is,  that  it  is  not  a 
solution  of  the  question, — it  is  not  a  direct  geometrical  construction ; 
for  it  must  be  repeated  an  infinite  number  of  times  to  yield  the  re- 
quired result.  As  an  approximation,  when  repeated  a  finite  num- 
ber of  times,  it  is  all  very  well,  but  of  no  particular  interest. 
This,  as  far  as  we  can  make  out,  is  the  one  grain  of  sense  in  the 
book.  For  the  rest,  it  is  marked  by  the  oddities  which  in  one  way 
or  another  the  whole  tribe  of  circle-squarers  displays.  Such  is  the 
picturesque  description  of  the  circle-squarer  holding  the  unwilling 
mathematician  "by  his  optical  sensorium  "  (p.  7).  The  position 
of  the  introduction,  which  is  printed  by  itself  on  the  last  page : 
and,  in  fact,  the  contents  of  the  book  generally,  are  odd ;  e.  g. 
on  p.  18  Mr.  Harris  gives  what  he  calls  "interrogative  proposi- 
tion X.,"  which  ends  thus  : — "  Shall  B  H,  the  part  so  cut  off  from 
the  straight  line  B  D,  be  the  required  line  equal  in  length  to  the  arc 
Bib?"  We  are  inclined  to  think  he  intends  this  solemn  question 
to  be  answered  in  the  affirmative ;  but  whether  this  be  so  or  not, 
there  is  no  sort  of  doubt  about  the  true  answer : — B  m,  an  eighth  part 
of  the  circumference,  is  0' 78540  times  the  radius,  while  an  easy  cal- 
culation shows  that  B  H,  determined  by  his  construction,  is  0*78361 
times  the  radius. 
On  the  whole,  should  the  book  fall  into  the  hands  of  any  of  our 
readers,  we  can  cordially  advise  them  not  to  waste  their  time  over  it. 
XLIX.  Proceedings  of  Learned  Societies, 
ROYAL  SOCIETY, 
[Continued  from  p.  313.] 
Nov.  23,  1871.— General  Sir  Edward  Sabine,  K.C.B.,  President, 
followed  by  Mr.  Francis  Galton,  Vice-President,  in  the  Chair. 
rPHE  following  communication  was  read  • — 
-*-      "Note  on  the  Spectrum  of  Encke's  Comet."     By  William 
Huggins,  D.C.L.,  LL.D.,  V.P.R.S. 
I  give  the  following  observations  of  Encke's  comet,  and  of  the 
spectrum  of  its  light,  in  the  order  of  the  dates  of  the  evenings  on 
which  they  were  made. 
Oct  17.  The  comet  presented  the  appearance  of  a  nearly  circular 
faint  nebulosity,  in  which  no  condensation  could  be  certainly  distin- 
guished. 
Nov.  7.  By  this  time  an  important  change  had  taken  place  in 
the  appearance  of  the  comet.  There  was  now  a  strong  condensation 
of  light  towards  the  east.  The  more  condensed  part  of  the  comet, 
which  was  fan-shaped,  was  bounded  on  the  eastern  side  by  a  tole- 
rably defined  contour,  which  approached  in  form  to  a  parabolic 
curve.     Surrounding  this  brighter  portion  of  the  comet  was  a  much 
