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M A G N E T I C I N T E N S I T Y .
a n d th e g e n e ra l re s u lts d e d u c e d fo r e a c h s tatio n . T h e c o lum n
e n title d “ T im e ” is th a t o f 3 0 0 v ib ra tio n s ; a n d th e “ C o rre c te d
T im e ” is th e m e a n o f th e se , c o rre c te d fo r th e ra te o f th e ch ro n o m
e te r a n d th e a rc , a n d re d u c e d to an a v e rag e tem p e ra tu re o f 60°.
T h e d ip s a re th o se o b serv ed b y C a p ta in F itz -R o y ; e x c e p t a t P o r t
F am in e , w h e re , as C ap ta in F itz -R o y d id n o t o b serve, i t has b e e n
s u p p lie d from C a p ta in K in g ’s o b s ervations ; a n d a t C o q u im b o ,
w h e re , fo r th e p u rp o s e o f c om p u tin g th e in te n s ity , i t h a s b e en
s u p p b e d b y e stim atio n from th e o th e r g e o g ra p h ic po sitio n s on th is
coast, a t w h ic h C ap ta in F itz -R o y o b serv ed th e d ip . In th e co lum n
s h ow in g th e tim e o f v ib ra tio n as a d ip p in g -n e e d le a t P lym o u th
c o rre sp o n d in g to th e p e rio d s o f o b serv atio n a t th e s ev e ra l s tations,
th e compensations h a v e h e e n in tro d u c e d fo r th e va ria tio n in th e
in te n s ity o f th e c y lin d e r, a g re e a b ly to w h a t h a s b e en said above on
th a t su b je c t. T h e tw o final c olumns e x h ib it th e va lu e s o f th e to ta l
m ag n e tic in te n s ity a t th e different stations d e riv e d from th e s e o b s e rva
tio n s. In th e first o f th e tw o columns, th e va lu e s a re g iv e n r e la tiv
e ly to th e fo rce a t P lym o u th , co n sid e re d as u n ity ; a n d in th e
s econd co lum n , re la tiv e ly to th e force a t P lym o u th , ex p re ss ed h y
1 37 5 • for th e p u rp o s e o f e x h ib itin g C ap ta in F itz -R o y ’s r e s u lts in
d ire c t compa rison w ith th e d e te rm in a tio n s o f c o n tin en ta l ob serv ers,
w h o h a v e ta k e n P a ris as th e ir basis, g iv in g th e fo rce a t P a n s th e
a rb itr a ry ex p re ss io n o f 1.3482. I h a v e ta k e n th e ra tio o f th e fo rc e
a t P lym o u th to th a t a t P a r is to b e as 1.375 to 1.348, w h ich I
b e liev e w ill p ro v e a v e ry n e a r a p p ro x im a tio n ; it is th a t w hich
r e s u lts from C ap tain F it z -R o y ’s o b serv atio n s a t P lym o u th , in
O c to b er 1836 (p a g e 1 7 ), a n d m in e , a t T o r tin g to n , in S ussex, in
J u n e 1837 (p a g e 10) ; th e d ip a t T o r tin g to n , a t th e p e rio d in
q u e stio n b e in g 68° 57', a n d th e in te n s ity , c om p a red w ith P a n s ,
th ro u g h th e m e d ium o f London, 1.368.
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