﻿xii 
  

  

  was 
  on 
  the 
  14th 
  of 
  October, 
  1820, 
  and 
  was 
  entitled 
  " 
  Memoir© 
  sur 
  une 
  

   Eormule 
  Generale 
  pour 
  determiner 
  la 
  surface 
  d'un 
  polygone 
  forme 
  sur 
  

   une 
  sphere 
  par 
  des 
  arcs 
  de 
  grands 
  ou 
  de 
  petits 
  cercles, 
  disposes 
  entre 
  

   eux 
  d'une 
  maniere 
  quelconque." 
  

  

  The 
  following 
  are 
  the 
  titles 
  of 
  other 
  papers, 
  also 
  read 
  in 
  the 
  Academy, 
  

   between 
  December 
  1820 
  and 
  February 
  1826 
  : 
  — 
  

  

  " 
  Sur 
  les 
  Conehoides 
  Circulaires." 
  Note 
  to 
  " 
  Memoire 
  sur 
  les 
  Caus- 
  

   tiques." 
  " 
  Memoire 
  sur 
  une 
  nouvelle 
  maniere 
  de 
  considerer 
  les 
  Caus- 
  

   tiques, 
  produites 
  soit 
  par 
  Eeflexion, 
  soit 
  par 
  Refraction." 
  " 
  Resume 
  

   d'une 
  nouvelle 
  The'orie 
  des 
  Caustiques, 
  suivi 
  de 
  diiferentes 
  applications 
  

   a 
  la 
  theorie 
  des 
  projections 
  stereographiques." 
  "Demonstration 
  et 
  deve- 
  

   loppements 
  de 
  la 
  theorie 
  des 
  Caustiques 
  se'condaires." 
  

  

  Quetelet's 
  researches, 
  already 
  noticed 
  by 
  G-ergonne 
  and 
  other 
  distin- 
  

   guished 
  geometricians, 
  were 
  particularly 
  remarked 
  on 
  by 
  Chasles, 
  after 
  

   the 
  - 
  Correspondance 
  Mathe'matique 
  et 
  Physique 
  ' 
  had 
  given 
  them 
  greater 
  

   publicity. 
  

  

  Two 
  other 
  memoirs 
  by 
  Quetelet, 
  inserted 
  in 
  the 
  collection 
  of 
  the 
  

   Academy, 
  still 
  remain 
  to 
  be 
  noticed 
  — 
  the 
  " 
  Memoire 
  sur 
  quelques 
  con- 
  

   structions 
  graphiques 
  des 
  orbites 
  planetaires" 
  and 
  the 
  "Memoire 
  sur 
  

   different 
  s 
  sujets 
  de 
  Geometrie 
  a 
  trois 
  dimensions." 
  

  

  The 
  1 
  Correspondance 
  Mathematique 
  et 
  Physique,' 
  already 
  mentioned, 
  

   was 
  commenced 
  by 
  Gamier 
  and 
  Quetelet 
  early 
  in 
  the 
  year 
  1825. 
  Its 
  

   contributors 
  were 
  dispersed 
  after 
  1830, 
  and 
  it 
  came 
  to 
  an 
  end 
  in 
  

   1839. 
  

  

  In 
  1822 
  Quetelet 
  went, 
  at 
  the 
  request 
  of 
  the 
  Academy, 
  with 
  M. 
  

   Kickx 
  to 
  explore 
  the 
  celebrated 
  grotto 
  known 
  as 
  the 
  Trou 
  de 
  Han, 
  and 
  

   they 
  drew 
  up 
  a 
  report 
  with 
  plates. 
  

  

  In 
  1824 
  it 
  was 
  proposed 
  that 
  Quetelet 
  should 
  extend 
  his 
  teaching 
  at 
  

   the 
  Athengeura, 
  so 
  as 
  to 
  include 
  Elementary 
  Physics, 
  Natural 
  History, 
  

   and 
  Chemistry. 
  About 
  the 
  same 
  time 
  M. 
  Thiry, 
  Professor 
  of 
  the 
  Higher 
  

   Mathematics, 
  resigned 
  his 
  post 
  ; 
  and 
  during 
  the 
  session 
  1824 
  and 
  1825 
  

   we 
  find 
  Quetelet 
  teaching 
  at 
  the 
  Athenaeuin 
  the 
  Descriptive 
  Geometry 
  

   of 
  Monge, 
  the 
  Theory 
  of 
  Shadows 
  and 
  Perspective, 
  and 
  the 
  Calculus 
  of 
  

   Probabilities 
  of 
  Lacroix. 
  He 
  also 
  gave 
  public 
  lectures 
  at 
  the 
  Museum 
  on 
  

   Experimental 
  Physics 
  and 
  on 
  the 
  Elements 
  of 
  Astronomy, 
  which 
  he 
  had 
  

   substituted 
  for 
  Natural 
  History 
  and 
  Chemistry. 
  He 
  had 
  two 
  classes, 
  

   which 
  he 
  conducted 
  simultaneously 
  in 
  adjoining 
  rooms, 
  passing 
  from 
  one 
  

   to 
  another, 
  and 
  perfect 
  order 
  is 
  said 
  to 
  have 
  reigned 
  in 
  each 
  . 
  His 
  teaching 
  

   is 
  described 
  as 
  simple 
  and 
  natural 
  : 
  his 
  arithmetical 
  instruction 
  was 
  

   founded 
  on 
  a 
  few 
  general 
  principles 
  ; 
  and 
  as 
  soon 
  as 
  his 
  pupils 
  were 
  ini- 
  

   tiated 
  into 
  algebraic 
  notation 
  and 
  its 
  first 
  rules, 
  he 
  showed 
  them 
  how 
  

   this 
  admirable 
  instrument 
  could 
  be 
  made 
  to 
  solve 
  ordinary 
  problems. 
  

   His 
  talent 
  for 
  drawing 
  was 
  evident 
  in 
  his 
  manner 
  of 
  tracing 
  his 
  geome- 
  

   trical 
  figures. 
  

  

  His 
  courses 
  of 
  Physics 
  and 
  Astronomy 
  at 
  the 
  Museum 
  attracted 
  large 
  

  

  