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been due to may iiaA'e want of practice iu
observing.
Should it turn out that Mr. Siemens’s instrument
can be thoroughly depended npon to give accurate
results it will undoubtedly be invaluable for certain
purposes. In our Antarctic cruise, for instance, on
several occasions the snrface-laj er was colder than
any layer heneatlx; our tliermometers on the Miller-
Casella construction registered accordingly tlieir
minimum on the surface, a warmer layer succeeded
in Avhich they registered their maximum, hut after
fixing these two points they were useless. A Avork-
ahle instrument on Mr. Siemens’s principle Avould
have given us the hottom temperature, which Ave
most of all desired.
I must say, however, that 1 donht if this resistance
apparatus can he applied in general practice to its
present purpose AA'ithout great modification. The
instrument is hulky, and, with the haltery and
galvanometer and thermometers and freezing mixture,
troublesome to Avoik on hoard a ship, and
difficult to observe if there is any motion. The
cahle is hulky and tender, and Avould prohahly not
stand the fatigue of heing often used as a sounding
line.
Throughout this section Mr. Buchanan has taken
the specific gravity of the sea-water from the surface
daily, and from the hottom and from intermediate
depths as often as it was possible to obtain samples.
A description of the instruments used in procuring
the water from the hottom and from intermediate
depths, and for determining the specific gravity, has
been already given (p. 34 et seq.).
I need only mention here that on the voyage from
Teneriffe to Sombrero Mr. Buchanan found the remarkable
and unexpected result that the water has
virtually the same specific gravity from the bottom
to Avithin 500 fathoms of the surface. Trom 500
fathoms the specific gravity rapidly rises, till it
usually attains its maximum at the surface. Some
minor variations in the specific gravity both of the
upper and of the lower layers have manifested themselves
from time to time, hut to these we shall refer
hereafter.
In the table of specific gravities appended, one or
two instances occur (marked Avith an asterisk on the
tahle) in which the specific gravity is as great at the
hottom as it is at the surface. In these cases aac are
forced to helieve that hy some misadventure the
cylinder of the water-hottle became disengaged just
as it reached the water. The lowering of the slip
water-hottle requires some care until it is fairly
beneath the surface, after which there is no chance
of the cylinder falling until the instrument reaches
t h e h o t t o m .
In t h i s o n r f ir s t s e c t io n a c r o s s t h e A t l a n t i c , t h e
d r e d g e Avas l o w e r e d t h i r t e e n t im e s , a n d n in e t im e s
b r o u g h t u p a s u f f i c i e n t s a m p l e o f t h e h o t t o m , c o n t
a in in g a n im a l s l i v i n g , o r Avhich h a d b e e n l i v i n g
Avhen t h e y e n t e r e d t h e d r e d g e ; fo r in m o s t c a s e s
w h e n b r o u g h t t o th e * s u r f a c e t h e y w e r e p e r f e c t ly d e a d .
Of t h e n in e s u c c e s s f u l h a u l s , f o u r w e r e in d e p th s
a h o v e 1500 f a t h o m s a n d u n d e r 2000, fo u r a h o v e
2000 a n d u n d e r 3000, a n d o n e in a d e p th o f 3150
f a th om s . In e a c h c a s e , w h a t Avitli t h e s la c k o f t h e
l in e a n d t h e m o v em e n t o f t h e s h ip , th e d r e d g e h a d t o
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