On  the  Spectroscopic  ObseiTation  of  the  Rotation  of  the  Sun.    47 
be  finite.  From  the  second  of  the  five  propositions  into  which 
he  divides  ray  argument  I  entirely  dissent.  I  do  not  hold  the 
opinion  (nor  have  I  anywhere  said  that  I  do),  that  "the  absolute 
motion  of  any  point  in  the  surface  of  a  glacier  is  proportional  to 
its  distance  from  the  Dearest  side  and  to  its  height  from  the  bot- 
tom of  the  channel." 
The  want  of  uniformity  from  centre  to  side  in  the  surface- 
motion  of  the  glacier  which  Mr.  Mathews  and  Mr.  Reilly  ob- 
served could  not  but  have  been  clue  to  irregularities  in  the  bot- 
tom of  its  channel,  or  in  its  sides,  or  in  its  direction  or  slope. 
It  has  apparently  escaped  Mr.  Mathews's  recollection  that  I 
reason  of  an  imaginary  glacier  of  homogeneous  ice  with  no  irre- 
gularities of  the  bottom  or  sides  of  its  channel  or  in  its  direction 
or  slope,  whose  surface- motion  from  centre  to  side  could  not  but 
be  uniform  as  to  the  two  sides.  If  it  be  true  that  a  glacier,  such 
as  this  imaginary  one,  could  not  descend  by  its  weight  only,  the 
conclusion  is  irresistible,  that  an  actual  glacier,  whose  channel 
is  irregular  as  to  its  surface,  direction,  and  slope,  could  not. 
I  have  endeavoured  to  make  intelligible  otherwise  than  in  the 
language  of  mathematical  science  a  mathematical  argument. 
On  reading  what  I  have  written  I  cannot  congratulate  myself  on 
ray  success.  Neither  party  to  an  argument  is  likely  to  be  con- 
vinced by  the  reasoning  of  the  other,  nor  is  any  valuable  result 
likely  to  be  arrived  at  by  them,  when  they  do  not  argue  in  the 
same  language. 
VI.   On  the  Spectroscopic  Observation  of  the  Rotation  of  the  Sunt 
and  a  new  Reversion- Spectroscope.     By  F.  Zollner*. 
IN  compliance  with  a  friendly  invitation,  I  repaired,  at  the 
Whitsuntide  vacation,  to  Bothkamp,  near  Kiel,  in  order  to 
take  in  hand,  at  Chamberlain  von  Billow's  splendidly  endowed 
private  observatory  there,  those  investigations  on  which  I  had  the 
honour,  two  years  since,  to  make  some  preliminary  communica- 
tions to  the  Society,  when  exhibiting  ray  reversion- spectroscope. 
The  large  refractor,  by  Schroder  of  Hamburg,  set  up  in 
Bothkamp,  and  furnished  with  an  excellent  clockwork,  is  not 
only,  after  the  Pulkowa  refractor,  the  largest  on  the  Continent, 
but  probably  takes  the  first  rank  among  all  the  refractors  of 
equal  size  by  its  high  optical  and  mechanical  finish.  Dr.  H.  C. 
Yogel  (the  director  of  the  observatory)  and  Dr.  Lohse,  as  assist- 
ant, in  acccrd  with  the  scientific  intention  of  the  founder,  have 
*  Translated  from  a  separate  impression,  communicated  by  the  Author, 
from  the  Berichte  der  Kbnigl.  Sdchsischen  Gesellschoft  der  Wissenschaften, 
Math.-Phys.  Classe,  for  July  1,  18/1. 
