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3 . Captain K in g ’s Observations o f D ip an d In te n s ity .
C ap ta in K in g , h a v in g h ith e r to m a d e k n ow n h is observ atio n s
w ith th e same c y lin d e r in th e y e a rs 1826 to 1830 only b y com m
u n ic a tin g th em to M. H a n s te e n , from w h om h e re c e iv ed th e
a p p a r a tu s , h a s n ow g iv en p e rm is sio n to C ap ta in F itz -R o y to
p u b lish th em w ith h is ow n. I h a v e a lre a d y n o tic e d th e g re a t
loss o f m a g n e tism w h ic h to o k p la c e in th is c y lin d e r d u r in g C ap ta
in K in g ’s v o y ag e , a n d th e c are w ith w h ic h th a t officer a v ailed
h im s e lf o f e v e ry o p p o rtu n ity o f a sc e rta in in g , b y d ire c t o b s e rv
a tio n , th e p ro p o rtio n o f th e loss su sta in ed in s e p a ra te p o rtio n s o f
th e vo y ag e. T h e r e a re tw e lv e statio n s o f o b s erv atio n on th e e ast
a n d w e s t coasts o f S o u th A m e ric a , b e sid e s th r e e statio n s in p o rts
o f th e A tla n tic on th e o u tw a rd v oyage. B y th e p ra c tic e o f r e p e a tin
g observ atio n s a t th e same s ta tio n a t d is ta n t in te rv a ls , th e S o u th
A m e ric a n statio n s a re so lin k e d to g e th e r a n d c o n n e c ted , th a t b y
a d o p tin g a m e th o d simila r to th a t u s e d in d e te rm in in g lo n g itu d e s
b y me an s o f c h ro n om e te rs, w e m a y com p u te th e in te n s ity a t a ll
th e S o u th A m e ric an statio n s re fe rr e d to a n d d e p e n d e n t on th e
fo rce a t R io d e J a n e iro ; re g a rd in g R io in th e same lig h t as a first
m e rid ia n is c o n sid e red in d e te rm in a tio n s o f lo n g itu d e . W e m a y
th e n m a k e R io th e m e an s o f c o n n e c tin g th e w h o le series w ith
E u ro p e -, fo r w h ic h it is rem a rk a h ly w e ll su ite d , th e in te n s ity th e r e
h a v in g b e en d e te rm in e d , in d e p e n d e n tly o f C ap tain K in g , b y
fo u r o bservers o f d ifferen t n a tio n s , wh o se re s u lts a re e x trem e ly
a c co rd an t.
T h e d ip o b s ervations o f C ap ta in K in g w e re com m u n ic a ted , in
occasional co rre sp o n d en c e d u r in g th e v o y ag e , to BI. H a n s te e n ,.
w h o c om p u te d th em b y B la y e r’s fo rm u la , a n d a r r a n g e d th em in
a ta b le , o f w h ic h a co p y was g iv e n b y C ap ta in K in g to C ap ta in
F it z -R o y , a n d is p r in te d in th e n e x t p a g e . A t some o f th e s ta tio
n s C ap ta in F it z -R o y also ob serv ed th e d ip in th e s u b s e q u e n t
v o y ag e, a n d , as w ill b e seen, th e re s u lts o f th e tw o o b s e rv e rs
sometimes differ co n sid e rab ly . T h is m a y h a v e b e e n c aused, e ith e r
by in s trum e n ta l o r o th e r e rro r o f o b s e rv a tio n , o r b y a c tu a l d ifferences
o f d ip e x is tin g in d iffe ren t localities a t th e same s tation.
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