An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

SOLAR SPOTS. 73
bo)th il formt and size. A. g. 27.
ipot somtctimes divides into
many s-maller oncs, and ag ain
a group may bte unitedt into a
silglec spot. Th'lte umrbra is la
-wide margin of lighter shlde,
and is conmnonlly of greater
extentt tthan thte nleus'the \
spots are usuall y confined to
a zone extending across trle
ccntlfai l rergiolns of thle sulln, Itot
excceediltn 60 in lreadtht. When the spots are obsel vedl from
dlay to day, tlhey arle seen to emove across the dtiskt o/t' te sum,
occupyintg a1bout two lwee1ks in p)tsslio fin om ole limnll to tite
othelr. After an absence of about the same period, tile spot
returns, Itavimng taken 27d. 711h. 37t1m. in the entire revolutiol,.
1 48. -1.Besides the fact of foreshlortening already mentaioned,
there is tanother proof that the spots are at tfre sMifirec of tho
nnll. Were tlley bodies lat La di.stanct ig. 28.
2'rom11 it, ite tintle during wi\ch they
would lbe seel ol the soltar disk wouldtttl
be less thanfli that occupied in the reaIainder of the r1'volutioln. T l us, let S
(l'ig. 2S) be the sutn, E, thle eartlt, and
ate tlhe path of the body rcvolving S
about the sun. Unless the spot were
nearly or quite ill contact withl the
body of thle st, being protjectcd upon
ls disk only while passing fi:om b to -
c, and being( invisible. fwhile describilng
tll a,e a t cab, it would of course be out
of' sig'lt loIger thant in sighlt, whereas
thele two periods are found to tle equal.
MoreooV er, the lines which all the solar
spots describe on tle( disk of tthe stu1
are folun to he parallel to ea:ch otler,
like tlhe circles of diunal revolutioll
art:,tound tthe earth; and }ten(ce it is infer':rt(ed that: theyr.arise from a simtilar cause, namely, thei?revol.S