﻿254 
  A. 
  M. 
  Mayer— 
  On 
  the 
  Flotation 
  of 
  

  

  less 
  than 
  the 
  breaking 
  weight. 
  If 
  from 
  any 
  cause, 
  such 
  as 
  the 
  

   gathering 
  of 
  dust 
  on 
  the 
  water, 
  or, 
  the 
  contamination 
  of 
  its 
  

   surface 
  from 
  the 
  vessel 
  holding 
  it, 
  the 
  surface 
  tension 
  should 
  

   be 
  weakened 
  19 
  per 
  cent, 
  then 
  the 
  unloaded 
  ring 
  will 
  sink. 
  

   This 
  weakening 
  of 
  the 
  surface 
  tension 
  is 
  readily 
  and 
  rapidly 
  

   brought 
  about 
  by 
  pouring 
  vapor 
  of 
  ether 
  on 
  the 
  water. 
  When 
  

   this 
  vapor 
  reaches 
  the 
  water 
  the 
  ring 
  moves 
  to 
  and 
  fro 
  in 
  a 
  

   tremulous 
  manner 
  and 
  then 
  sinks. 
  

  

  In 
  my 
  ignorance, 
  I 
  saw 
  in 
  these 
  experiments 
  a 
  property 
  of 
  

   flotation 
  peculiar 
  to 
  aluminum. 
  Experiment, 
  however, 
  soon 
  

   showed 
  me 
  that 
  all 
  metals, 
  with 
  clean 
  surfaces, 
  from 
  platinum 
  

   of 
  a 
  density 
  of 
  21*5 
  to 
  magnesium 
  of 
  a 
  density 
  of 
  1*7, 
  float 
  on 
  

   w 
  T 
  ater. 
  When 
  and 
  with 
  whom 
  originated 
  the 
  erroneous 
  state- 
  

   ment, 
  that 
  metals 
  to 
  float 
  must 
  have 
  their 
  surfaces 
  greased, 
  I 
  

   have 
  not 
  been 
  able 
  to 
  discover 
  ; 
  but 
  this 
  error 
  has 
  been 
  copied 
  

   from 
  one 
  treatise 
  on 
  physics 
  into 
  another 
  for 
  about 
  a 
  century. 
  

   The 
  older 
  writers, 
  and 
  those 
  who 
  in 
  recent 
  times 
  have 
  pub- 
  

   lished 
  papers 
  on 
  their 
  studies 
  of 
  these 
  phenomena, 
  make 
  no 
  

   mention 
  of 
  the 
  necessity 
  of 
  greasing 
  a 
  metal 
  to 
  make 
  it 
  float. 
  

  

  In 
  his 
  " 
  History 
  of 
  Physics 
  "* 
  Pdggendorff 
  states 
  that 
  

   "Norman 
  (he 
  who 
  discovered 
  the 
  dip 
  of 
  the 
  needle) 
  showed 
  

   Gilbert 
  that 
  a 
  needle 
  placed 
  carefully 
  on 
  water 
  floats, 
  and 
  if 
  

   magnetized 
  points 
  constantly 
  in 
  one 
  direction." 
  Poggendorff 
  

   does 
  not 
  give 
  his 
  authority 
  for 
  this 
  statement. 
  Gilbert 
  in 
  his 
  

   "De 
  Magnete," 
  1600, 
  does 
  not 
  say 
  that 
  Norman 
  floated 
  a 
  metal 
  

   per 
  se 
  on 
  water. 
  He 
  thus 
  describes 
  Norman's 
  experiment 
  : 
  

   "Norman 
  proves 
  his 
  theory 
  as 
  follows: 
  Take 
  a 
  round 
  vessel 
  

   full 
  of 
  water; 
  on 
  the 
  mid 
  surface 
  of 
  the 
  water 
  float 
  a 
  small 
  

   bit 
  of 
  iron 
  wire 
  supported 
  by 
  just 
  as 
  much 
  cork 
  as 
  will 
  keep 
  it 
  

   afloat 
  while 
  the 
  water 
  is 
  in 
  equilibrium 
  : 
  the 
  wire 
  must 
  have 
  

   been 
  first 
  magnetized 
  so 
  as 
  to 
  show 
  plainly 
  the 
  variation 
  point 
  

   D. 
  . 
  ."f 
  It 
  may 
  be 
  that 
  Norman's 
  experiment 
  of 
  floating 
  a 
  

   needle 
  is 
  described 
  in 
  his 
  " 
  New 
  Attractive," 
  1596, 
  a 
  very 
  rare 
  

   work, 
  which 
  I 
  have 
  not 
  been 
  able 
  to 
  consult 
  

  

  "The 
  observation 
  of 
  Norman, 
  that 
  a 
  steel 
  needle 
  placed 
  

   carefully 
  on 
  water 
  floats, 
  led 
  Borelli, 
  1655, 
  to 
  study 
  more 
  

   minutely 
  this 
  phenomenon. 
  He 
  procured 
  two 
  little 
  sheets 
  of 
  

   brass, 
  and 
  placed 
  them 
  with 
  care 
  on 
  water, 
  where 
  they 
  floated. 
  

   By 
  means 
  of 
  rods 
  he 
  pushed 
  them 
  towards 
  one 
  another, 
  and 
  

   saw 
  that 
  when 
  they 
  had 
  approached 
  sufficiently, 
  they 
  mutually 
  

   attracted.";); 
  

  

  Descartes 
  in 
  " 
  Les 
  Meteores," 
  Leyden, 
  1638, 
  says 
  :§ 
  " 
  La 
  

   superficie 
  de 
  l'eau 
  est 
  beaucoup 
  plus 
  malaysee 
  a 
  diuiser 
  que 
  

  

  * 
  Histoire 
  de 
  la 
  Physique, 
  Paris, 
  1883, 
  p. 
  170. 
  

  

  \ 
  "De 
  Magnete." 
  Translation 
  by 
  P. 
  Fleury 
  Mottelay, 
  p. 
  244. 
  N. 
  Y., 
  1893. 
  

  

  \ 
  Poggendorff 
  : 
  Hist, 
  de 
  la 
  Phys.. 
  p. 
  249. 
  

  

  § 
  I 
  give 
  this 
  quotation 
  in 
  the 
  orthography 
  of 
  his 
  time. 
  

  

  