38 
REPORT— 1847. 
for the primary rays of the spectrum, seems to be a point but little understood, lb 
following are a few cases in which the well-known accuracy of the obsoTEis sit 
satisfy us as to the correctness of the data, but in which some remarkable aaosile 
appear : — 
llcdium. 
Index for 
White Light 
Indices for 
Sundud Raji 
(Rudberg]. 
XeaL of 
ezntnt 
Isdiees. 
Quartz, 
ordinary ray. 
Quartz, 
extraordinary ray. 
Calc-spar, 
ordinary ray. 
Calc-spar, 
extraordinary rav. 
j- 1-5484 1 
1 1-5582 1 
1 1-6543 j 
J- 1-4833 1 
E. .. r54yi 
F. .. 1*5496 
E. .. 1-5563 
F. .. 1-5589 
B. .. 1-6531 
C. .. 1-6545 
K... 1-6680 
B... 1-4839 
K... 1-4907 
1 1-6495 
1 1-5588 
.1-6682 
j- 1-4903 
or 
border v.wv, a pait ut tuu specLrum wuifu tuu ua 
sense ^ the mean and far from the most illuminating part. . 
In the two latter cases, an<l more especially in the last, the deviation is 
striking ; the mfan ray corresponding to the /nil red in one case, and e»en « 
loicfat part of the red in the other; while in either case the numerical w®'',. 
extreme indices agrees closely with the observed index for F, at the junction oiw 
gfwn and blue space.H. 
anomalies are probably connected with those yetnnkswuF^ 
tvibM m the nature of dispersion which occasion the primary paradox, tist 
^L. 8 ‘vg perfectly pure rays of the same colour in widely ^ 
wi, these spectra are recompounded, in all cases 
wh te light 18 reproduced ; a paradox, w’hich. though now (uUy evinced in- 
«n. ' .'^ouj’tlfss the real ground of Newton’s so positive denial of the W» 
tuiproporUonal dispersion. 
Oh Me Electric Current hy which the PhmioTmm of Terresiriai 
may he prodttced. Ey Professor Thomson. 
nf thwera, first demonstrated by Green, that the actionrf^ 
dutrlKuti external point, may be represented by 
that n same kind over the surface of the body I 
which will'll'^ distribution of matter over the surface of a body in*yj» « 
of exactly the same force, whether of gravitation, of 
ie?D ■"««> by «pplrbg thislheo^^* 
certain .iW considered is that of terrestrial magnetism. ^ 
ni? " ‘wagioary magnetic matter mar be found. M 
o^?hJv terrestrial mognefisro obser^-ed at the surib« J! 
nefism 5 r ’ are duo to atmospheric or e.Ttemal 
^^no 'i« pro|> 08 ition. aJthSueh of great th««t.c*l 
which as expressmg a physical fact; for there arc 
either imn internal sources of terrestrial mi^nelism to exist- ^ j 
mwiuet r>r®«? 't “ or in part a » 
eoSKi * “/ ""f '"“coive it to be an electro- m4nct, with or^J, 
^cond hJ£iT,l?5 magnetism. In the present stale of ^oixj 
*^a»ona be the more probable j and indeed we have 
wholly or in^iIarMh^ terrestrial electric curreatfeg^ji^ 
it becomes an phacnomcna, is a physical fact. 
actual i>hajnomo!fr*^"® question, whether mere electric currents couW ^ gi 
•ftirmative answer electro-magnetic theory 
''cr, but an answer which must be regarded as merely “> 
