346     M.  F.  Zollner  on  the  Origin  of  the  Earth's  Magnetism, 
nerally  speaking,  only  four  properties  of  the  sun  are  necessary 
and  sufficient  to  account  for  all  essential  phenomena  hitherto 
observed  on  the  sun.     These  properties  are  the  following  :— 
1.  Intense  radiation  of- heat  from  the  sun. 
2.  Its  rotation. 
3.  The  existence  of  an  atmosphere. 
4.  The  liquid  condition  of  the  solar  surface. 
The  first  three  of  these  properties  are  to  be  regarded  as  facts 
proved  by  observation ;  and  I  deduced  the  fourth  as  a  necessary 
consequence  of  the  eruptive  character  of  a  great  many  protu- 
berances*. 
Kespighi,  who  has  carefully  observed  numerous  protuber- 
ances, has  been  led  to  consequences  which  agree  perfectly  well 
with  the  views  which,  as  he  expressly  remarks,  have  been  hitherto 
maintained  by  myself  alone f,  as  regards  the  liquid  condition  of 
the  sun's  surface  as  well  as  the  nature  of  the  sun-spots  J, 
*  See  Proceedings  of  the  Royal  Saxon  Society  of  Sciences,  June  2nd, 
1870.  In  my  paper  then  communicated,  "  On  the  Temperature  and  Phy- 
sical Condition  of  the  Sun's  Surface,"  I  made  the  following  remarks  : — 
"  Without  stepping  beyond  the  range  of  known  analogies,  and  therefore  of 
conditions  explanatory  of  cosmical  phenomena,  it  is  scarcely  possible  to  find 
a  cause  for  these  eruptive  protuberances  other  than  that  of  a  difference  of 
pressure  between  the  gases  in  the  interior  and  those  on  the  surface  of  the 
sun.  The  possibility  of  such  a  difference  of  pressure,  however,  necessitates 
the  existence  of  a  zone  of  separation  between  the  interior  and  exterior 
masses  of  hydrogen,  the  latter  of  which  have  been  shown  to  form  an  essen- 
tial part  of  the  solar  atmosphere. 
t  M.  Emile  Gautier,  also,  up  to  the  year  1869,  considered  the  sun-spots 
to  be  solid  slag-like  masses.  But  in  a  paper  published  in  the  Archives  de 
Geneve  (August  1869)  he  abandons  this  view  in  favour  of  a  more  nebulous 
nature  of  the  sun-spots,  influenced  by  the  opinion  of  Secchi  and  Faye.  A 
discussion  of  my  law  of  the  sun's  rotation  by  E.  Gautier,  which  I  receive 
whilst  this  paper  is  being  printed,  closes,  however,  with  the  following 
words : — 
"  Notre  observation  ne  porte  du  reste,  que  sur  un  detail  peu  essentiel  a 
la  theorie  de  M.  Zollner.  Celle-ci  n'en  reste  pas  moins  la  seule  jusqu'a  ce 
jour,  qui  s'assimile  d'une  maniere  aussi  complete  aux  circonstances  connues 
dela  physique  solaire,  sans  etre  obligee  de  recourir  a  des  suppositions  tout 
a  fait  en  dehors  des  notions  generates  admises  dans  la  physique  terrestre." 
%  Respighi, "  Sulle  Osservazioni  spettroscopiche  del  bordo  e  delle  protu- 
beranze  solari"  etc.,  Atti  della  Reale  Accademia  dei  Lincei  nella  sessione 
I.,  del  4  decembre,  1870. 
The  following  passages  confirm  what  I  said  above  : — 
"  La  straordinaria  violenza  o  velocita  di  tali  eruzioni  ci  prova  che  questi  gas 
debbono  trovarsi  ad  uno  stato  di  enorme  tensione,  e  che  percio  essi  debbono 
trovarsi  ivi  imprigionati  o  compressi  dalla  resistenza,  o  dal  peso  di  uno 
strato  od  inviluppo  esteriore  di  conveniente  spessezza  e  densita 
"  Non  resta  quindi  che  la  supposizione  di  uno  strato  o  inviluppo  liquido, 
col  quale  potrebbero  conciliarsi  tutte  queste  particolarita."  (P.  41.) 
"  Quantunque  io  prevegga  che  queste  conclusioni  incontreranno  forti  ed 
autorevoli  opposizioni,  pure  ho  stimato  opportuno  di  riferirle,  perch  e  mi  si 
