﻿Notices 
  respecting 
  New 
  Boohs. 
  351 
  

  

  [Added 
  June 
  11, 
  1908.] 
  — 
  It 
  may 
  be 
  noticed 
  that 
  under 
  

   the 
  radial 
  (central) 
  action 
  of 
  its 
  own 
  gravitational 
  forces, 
  a 
  

   mass 
  of 
  matter, 
  by 
  mere 
  increase 
  of 
  size, 
  — 
  becomes 
  elastic. 
  

   The 
  forcible 
  recovery 
  o£ 
  the 
  spherical 
  form, 
  under 
  the 
  radial 
  

   stress, 
  amounts 
  substantially 
  to 
  a 
  power 
  of 
  elastic 
  restitution. 
  

  

  Let 
  us 
  suppose 
  a 
  nebula, 
  instead 
  of 
  consisting 
  of 
  those 
  

   smaller 
  fragments 
  o£ 
  material 
  to 
  which 
  we 
  apply 
  the 
  name 
  

   " 
  meteorites/' 
  after 
  disintegration 
  in 
  our 
  atmosphere, 
  — 
  to 
  be 
  

   constituted 
  of 
  masses 
  more 
  comparable 
  to 
  the 
  earth 
  in 
  size 
  

   [small 
  in 
  relation 
  to 
  the 
  solar 
  dimensions] 
  : 
  — 
  these 
  energetic 
  

   bodies 
  automatically 
  setting 
  up 
  that 
  equilibriated 
  movement 
  

   among 
  themselves 
  characteristic 
  of 
  the 
  (minuter) 
  particles 
  of 
  

   a 
  gas. 
  Then 
  such 
  gravitationally-elastic 
  portions 
  of 
  material 
  

   constituting 
  an 
  attenuated 
  nebula, 
  and 
  surviving 
  without 
  

   encounters 
  for 
  lengthy 
  time-periods, 
  would 
  strive 
  to 
  conserve 
  

   the 
  natural 
  globular 
  form 
  [vibrating 
  about 
  the 
  same], 
  con- 
  

   ditioned 
  by 
  the 
  powerful 
  radial 
  stress 
  of 
  gravity 
  in 
  each 
  case: 
  

   but 
  coalescence 
  into 
  larger 
  masses 
  (spherical) 
  now 
  and 
  then, 
  

   by 
  relaxation 
  of 
  the 
  translatory 
  motion, 
  is 
  of 
  course 
  not 
  

   excluded. 
  

  

  An 
  inert 
  mass 
  of 
  (say) 
  the 
  solar 
  diameter, 
  if 
  we 
  suppose 
  

   broken 
  up 
  by 
  a 
  quick 
  encounter, 
  would 
  then, 
  even 
  if 
  cold 
  

   and 
  solidified 
  throughout, 
  resolve 
  itself 
  into 
  globular 
  frag- 
  

   ments, 
  and 
  not 
  into 
  portions 
  of 
  irregular 
  shape, 
  — 
  excepting 
  

   those 
  splinters 
  below 
  a 
  certain 
  limit 
  of 
  size. 
  

  

  And 
  this 
  would 
  doubtless 
  be 
  the 
  essential 
  primary 
  stage 
  of 
  

   such 
  a 
  cosmic 
  encounter 
  : 
  — 
  a 
  truly 
  gaseous 
  nebula 
  demanding 
  

   time 
  to 
  constitute 
  itself. 
  It 
  appears, 
  accordingly, 
  that 
  the 
  

   translatory 
  energy 
  of 
  the 
  encounter 
  would 
  at 
  first 
  continue 
  

   mainly 
  as 
  mass-motion 
  : 
  — 
  passing 
  more 
  gradually 
  into 
  the 
  

   finer 
  motion 
  of 
  molecules. 
  

  

  XXVIII. 
  Notices 
  respecting 
  New 
  Books. 
  

  

  A 
  Treatise 
  on 
  Hydraulics. 
  By 
  William 
  Cawthorne 
  TTnwix, 
  

  

  LL.D., 
  F.R.S. 
  London 
  : 
  A. 
  & 
  C. 
  Black. 
  1907. 
  

   r 
  PHIS 
  book 
  may 
  in 
  a 
  sense 
  be 
  regarded 
  as 
  a 
  new 
  edition 
  of 
  the 
  

   -*- 
  valuable 
  article 
  contributed 
  by 
  Professor 
  Unwin 
  to 
  the 
  Ency- 
  

   clopaedia 
  Britannica 
  more 
  than 
  thirty 
  years 
  ago. 
  Certain 
  para- 
  

   graphs 
  and 
  many 
  of 
  the 
  diagrams 
  are 
  simply 
  reproduced, 
  but 
  the 
  

   omission 
  of 
  much 
  of 
  the 
  former 
  detail 
  and 
  the 
  substitution 
  of 
  

   more 
  recent 
  data, 
  with 
  a 
  complete 
  recasting 
  of: 
  many 
  essential 
  parts, 
  

   make 
  the 
  treatise 
  an 
  altogether 
  new 
  work. 
  To 
  one 
  familiar 
  with 
  

   the 
  article 
  of 
  1867, 
  a 
  glance 
  through 
  the 
  book 
  will 
  reveal 
  many 
  

   similarities 
  ; 
  but 
  a 
  careful 
  inspection 
  will 
  show 
  that 
  there 
  are 
  many 
  

   more 
  differences, 
  and 
  that 
  Professor 
  Unwin 
  has 
  spared 
  no 
  pains 
  

   to 
  bring 
  his 
  work 
  up 
  to 
  date. 
  A 
  complete 
  chapter 
  on 
  the 
  distri- 
  

  

  