and  the  Magnetic  Relations  of  the  Heavenly  Bodies.        467 
days. 
From  the  declination  at  Prague  in  1870  (calculated)   T  =  26'69 
„         (graphically)    „  26-20 
„  „  Vienna  in  1870  (calculated)     „  26*39 
„        dip  at  Prague  in  1870     .     .     (calculated)     „  26*03 
The  mean  value, 
T  =  26-33  days, 
may  be  regarded  as  the  most  probable  duration  of  the  period, 
and  hence  as  the  result  of  the  first  attempts  to  calculate  the  syno- 
dical  time  of  rotation  of  the  sun  by  the  aid  of  the  magnetic 
needle. 
"  The  true  time  of  rotation  of  the  sun  is  found  from  this  to 
be  =24*55  days,  or  almost  exactly  the  same  as  the  time  of  re- 
volution of  the  sun-spots  near  the  equator  as  found  by  the 
astronomical  observations  of  Sporer. 
"  I  have  represented  graphicall)7,  and  investigated  with  refer- 
ence to  the  264--day  period,  a  series  of  magnetical  observations 
at  Prague,  Vienna,  Kremsmiiuster,  Dublin,  Toronto,  St.  Helena, 
&c,  extending  over  several  years ;  and  I  have  partly  subjected 
them  to  calculation." 
The  two  Plates  which  accompany  the  paper,  and  cannot  here 
l>e  reproduced,  show  graphically  the  periodicity  mentioned.  To 
the  values  of  a  dotted  line  constructed  by  means  of  the  mean 
monthly  values  of  declination  Hornstein  added  the  periodical 
oscillation,  and  joined  the  points  so  found  by  a  red  line.  He 
remarks  as  follows  with  reference  to  this  line  : — 
"  In  this  way  the  red  line  was  drawn,  which  (with  unimportant 
exceptions  at  the  end  of  1869)  is  in  harmony  with  the  real  course 
of  the  declination  as  far  back  as  the  beginning  of  1869,  or  twenty 
full  rotations  of  the  sun  before  the  middle  of  1870.  This  is  a 
confirmation  of  the  supposition  that  through  many  rotations  the 
sun  was  in  a  state  of  quietness,  in  consequence  of  which,  in  spite 
of  great  revolutions,  the  same  part  exerted  always  about  the  same 
influence." 
I  have  taken  the  liberty  to  give  in  detail  this  important  and, 
for  the  understanding  of  the  magnetic  relations  existing  between 
sun  and  earth,  most  valuable  research  of  Hornstein,  because, 
besides  its  general  importance,  it  is  a  proof  for  the  views  here 
developed  on  the  physical  origin  of  the  magnetic  action  of  the 
heavenly  bodies. 
It  is,  however,  easily  shown  that  the  occurrences  on  the  sun's 
surface  which  Hornstein  mentions  at  the  beginning  of  his  paper 
cannot  be  the  cause  of  the  discovered  periodicity;  for,  besides 
the  difficulty,  admitted  by  himself,  of  thereby  explaining  the 
constancy  of  the  magnetic  action  of  a  definite  point  of  the  sun's 
surface,  there  are  many  reasons  against  it. 
2H2 
