﻿SOLAR 
  RADIATION 
  AS 
  A 
  POWER 
  SOURCE 
  — 
  ABBOT 
  103 
  

  

  could 
  readily 
  be 
  attained, 
  this 
  is 
  not 
  advantageous. 
  For 
  though 
  the 
  

   thermodynamic 
  efficiency 
  factor 
  Tx 
  — 
  T 
  2 
  /T 
  x 
  would 
  gain, 
  this 
  would 
  

   be 
  more 
  than 
  offset 
  by 
  the 
  increased 
  heat 
  losses 
  of 
  the 
  boiler. 
  Fur- 
  

   thermore, 
  though 
  quartz 
  glasses 
  like 
  Pyrex 
  enable 
  us 
  to 
  use 
  transpar- 
  

   ent 
  evacuated 
  sheaths 
  at 
  fairly 
  high 
  temperatures, 
  high 
  vacua 
  lose 
  

   their 
  excellence 
  with 
  very 
  high 
  temperatures, 
  so 
  that 
  convection 
  

   becomes 
  serious. 
  

  

  On 
  these 
  accounts 
  it 
  is 
  not 
  desirable 
  in 
  solar-power 
  machines 
  to 
  

   employ 
  boiler 
  temperatures 
  much 
  above 
  200° 
  C. 
  (392° 
  F.). 
  If 
  oper- 
  

   ating 
  to 
  a 
  condenser 
  at 
  30° 
  C, 
  such 
  a 
  temperature 
  of 
  the 
  boiler 
  gives 
  

   a 
  thermodynamic 
  factor 
  of 
  473 
  — 
  303/473=36 
  percent, 
  which, 
  for 
  

   reasons 
  just 
  explained, 
  may 
  be 
  regarded 
  as 
  the 
  maximum 
  to 
  be 
  ex- 
  

   pected 
  if 
  due 
  regard 
  is 
  paid 
  to 
  loss 
  of 
  heat 
  from 
  the 
  boiler. 
  

  

  Another 
  fundamental 
  consideration 
  in 
  designing 
  solar-power 
  de- 
  

   vices 
  is 
  that 
  the 
  loss 
  of 
  heat 
  from 
  a 
  body 
  through 
  convection 
  or 
  radia- 
  

   tion 
  is 
  directly 
  proportional 
  to 
  the 
  external 
  area 
  of 
  the 
  surface 
  of 
  the 
  

   body. 
  Hence 
  it 
  is 
  of 
  importance 
  for 
  diminishing 
  the 
  waste 
  of 
  heat 
  

   that 
  the 
  boiler 
  surface 
  should 
  be 
  as 
  small 
  as 
  possible, 
  by 
  using 
  fairly 
  

   accurate 
  optical 
  mirror 
  forms. 
  

  

  Astronomers 
  have 
  long 
  ago 
  agreed 
  that 
  the 
  simplest 
  mechanical 
  

   motions 
  that 
  could 
  be 
  devised 
  for 
  following 
  celestial 
  objects 
  are 
  those 
  

   of 
  the 
  equatorial 
  telescope. 
  This 
  scheme 
  involves 
  mounting 
  the 
  in- 
  

   strument 
  which 
  is 
  to 
  follow 
  the 
  celestial 
  object 
  upon 
  an 
  axis 
  parallel 
  

   to 
  the 
  earth's 
  axis, 
  and 
  imparting 
  to 
  this 
  "polar 
  axis" 
  a 
  uniform 
  

   motion 
  of 
  15° 
  per 
  hour. 
  If 
  the 
  instrument 
  is 
  to 
  be 
  adapted 
  to 
  follow 
  

   objects 
  at 
  different 
  distances 
  north 
  or 
  south 
  of 
  the 
  celestial 
  equator 
  — 
  

   that 
  is, 
  of 
  different 
  declinations 
  — 
  there 
  must 
  be 
  a 
  second 
  axis 
  at 
  right 
  

   angles 
  carried 
  by 
  the 
  polar 
  axis. 
  This 
  second 
  axis, 
  called 
  the 
  decli- 
  

   nation 
  axis, 
  carries 
  the 
  telescope 
  or 
  other 
  following 
  device 
  and 
  is 
  to 
  

   be 
  set 
  by 
  hand 
  to 
  the 
  position 
  of 
  any 
  desired 
  celestial 
  object, 
  and 
  

   clamped 
  there. 
  If 
  the 
  sun 
  remained 
  stationary 
  with 
  regard 
  to 
  the 
  

   celestial 
  equator, 
  no 
  second 
  axis 
  would 
  be 
  needed 
  in 
  solar-power 
  ma- 
  

   chines. 
  But 
  the 
  sun 
  travels 
  through 
  47° 
  north 
  and 
  south 
  during 
  the 
  

   year. 
  

  

  It 
  is 
  highly 
  desirable 
  to 
  operate 
  with 
  a 
  stationary 
  boiler. 
  The 
  

   withdrawal 
  of 
  steam 
  from 
  a 
  moving 
  boiler 
  involves 
  costly 
  and 
  un- 
  

   satisfactory 
  connection. 
  It 
  is 
  clear 
  that 
  a 
  spherical 
  boiler 
  placed 
  

   in 
  the 
  intersection 
  of 
  the 
  two 
  axes 
  of 
  an 
  equatorial 
  mirror 
  mounting 
  

   could 
  be 
  stationary. 
  But 
  it 
  would 
  be 
  impossible 
  to 
  enclose 
  thoroughly 
  

   with 
  an 
  evacuated 
  sheath. 
  The 
  mirror 
  in 
  this 
  case 
  would 
  be 
  circu- 
  

   lar 
  and 
  preferably 
  of 
  parabolic 
  curvature, 
  which 
  is 
  an 
  awkward 
  

   shape 
  for 
  fabrication. 
  

  

  It 
  has 
  seemed 
  to 
  me 
  preferable 
  to 
  neglect 
  the 
  north-to-south 
  mo- 
  

   tion 
  of 
  the 
  sun, 
  using 
  a 
  mirror 
  rotating 
  uniformly 
  at 
  15° 
  per 
  hour 
  

  

  