Aug. 25, 1870] 
NATURE 
335 
indicates. That a large proportion of it is deflected back towards 
the Equator is universally admitted, and that the remainder can 
be gathered together after its initial velocity has been expended, 
and forced downwards so as to displace colder water to the depth 
of 800 fathoms whilst still moving north-east, seems to me in the 
highest degree improbable. 
To what then is the north-east movement of the warm upper 
stratum of the North Atlantic attributable? I have attempted 
to show that it is part of a general interchange between Polar and 
Equatorial waters, which is quite independent of any such local 
accidents as those that produce the Gulf-Stream proper, and 
-which gives movement to a much larger and deeper body of 
water than the latter can affect. The evidence of such an inter- 
change is twofold—that of physical theory and that of actual 
observation. Such a movement must take place, as was long 
since pointed out by Prof. Buff, whenever an extended body of 
water is heated at one part and cooled at another ; it is made use 
of in the warming of buildings by the hot-water apparatus, and it 
was admirably displayed at the Royal Institution a few months 
since in the following experiment kindly prepared for me by 
Dr. Odling :—A long but very narrow trough, with plate-glass 
sides, having been filled with water, a tube into which a steam- 
jet was conveyed was introduced vertically at one end, whilst a 
lump of ice was wedged between the sides of the trough at its 
opposite extremity. Some red colouring matter mixed with gum, 
of such viscidity as to be carried along by any movement of the 
liquid mass without mingling with it, was introduced into the 
water at the end of the trough warmed by the steam-jet, and a 
like mixture of a blue colour was introduced at the end cooled 
by the ice. The latter very speedily sank to the bottom along 
the side of the ice-wedge, and then crept slowly along the floor 
of the trough, towards its warm end, where it rose along the side 
of the heated tube until it reached the surface, and then slowly 
flowed back towards the cold extremity. On the other hand the red 
liquid passed slowly along the surface in the first instance from the 
warm to the cold extremity, then sank (as the blue had previously 
done), crept along the surface of the blue layer covering the bottom 
of the trough, and then rose (as the blue had previously done) 
along the side of the heated tube to the surface. Thus a circu- 
lation was shown to be maintained in the trough by the applica- 
tion of heat at one of its extremities and of cold at the other, the 
heated water flowing along the surface from the warm to the cold 
end, and the cooled water flowing along the dottom from the cold 
to the warm end: just as it is here maintained that Equatorial 
water streams on the surface towards the Poles, and that Polar 
water returns along the bottom towards the Equator, if the 
movement be not interfered with by interposed obstacles, or pre- 
yented by antagonistic currents arising from local peculiarities. 
So far is this from being the case with the general surface-move- 
ment in the Atlantic basin, that it will concur with and supple- 
ment the motion of the Gulf-Stream proper, which may thus be 
regarded as a portion of the general Equatorial-polar current, 
deflected in the first instance by the action of the trade-winds, 
but subsequently rejoining the great body of water having a 
north-east motion of its own and imparting to its surface-layer a 
higher temperature than it would otherwise convey. 
Now that this hypothesis is at any rate deserving of considera- 
tion, and is not to be dismissed by the ¢fse dixit even of so high 
an authority as Dr. Petermann, though backed by my excellent 
colleague, I venture to maintain on the strength of the parallel 
case afforded by the temperature-phenomena of the Southern 
Indian Ocean. For, as Capt. Maury has shown, a definite 
current exists in the midst of it, carrying tropical waters far into 
the southern temperate zone, and not attributable to any such 
local peculiarities as those which produce the Gulf-Stream of the 
Atlantic. Conversely, the Hydra soundings in the Arabian 
Gulf have given evidence of a northerly reflux of glacial water 
from the Antarctic basin along the deep-sea bed of the Indian 
Ocean to replace the more superficial stratum which has moved 
southwards. This glacial water will in its turn be raised from 
the depths by the heating action of the tropical sun, and then 
return as the southerly surface-stream to the Antarctic basin, 
and would there sink by surface-cooling and again flow north- 
wards along the sea-bed. 
The facts of observation, then, being in the case last cited 
entirely accordant with physical theory, I submit that the same 
theory may be fairly applied to the explanation of those tempera- 
ture-phenomena of the North Atlantic, which (as it seems to me) 
cannot be more than very partially, if at all, accounted for by the 
agency of the Gulf Stream proper. And Iam content to leave it 
to the judgment of those who are competent to deal with the 
question whether the north-east movement of the vast breadth of 
water lying between the coast of Greenland and that of Northern 
Europe, usually extending to a depth of 5,000 feet, is more 
likely to depend upon an impetus derived from a portion of the 
comparatively narrow and shallow current which issues from the 
Narrows thousands of miles off, or to form part of a general 
circulation of oceanic water, the cause of which is quite inde- 
pendent of local accidents. 
The readers of NATURE will, I am sure, join with me in deeply 
regretting that Prof. Wyville Thomson is prevented by illness 
from taking that share in the scientific exploration of the Medi- 
terranean basin, now about to commence, which has conduced 
so greatly to the success of the two previous expeditions in which 
we have had the pleasure and advantage of being fellow- 
workers. 
Gibraltar, Aug. 11 WILLIAM B. CARPENTER 
Dr. Hooker’s ‘“‘Student’s Flora” 
ALL the reviews which I have read of the ‘*Student’s Flora 
of the British Islands” are, as they undoubtedly should be, ap- 
preciative, but your reviewer has done well in pointing out a few 
seeming discrepancies, which it would, perhaps, be well if 
attended to in a second edition ; and, if you will permit space, I 
will endeavour briefly to add to your list of desiderata. In the 
first place I take it that a good glossary is an essential, if not an 
absolute necessary, adjunct to a students’ manual; yet we look 
in vain for anything of the kind in Dr. Hooker’s new ‘ Flora.” 
Dr. Hooker could scarcely have thought beginners in botany 
able to interpret many words used by him in his generic and 
specific descriptions. I am also sorry to see that little word 
“sub” used so extensively ; for my own part I do not under- 
stand its meaning as applied in zoology and botany. I can quite 
understand its applied use in sub-contractor, sub-lieutenant, sub- 
terranean, &c., but who dares tell us that one tribe, or one 
family, or genus, or species is subordinate to another? I com- 
prehend a ‘‘species” as a form of animal or vegetable life which 
differs slightly but materially and permanently from its nearest 
ally ; such a form is, in my humble opinion, worthy to hold 
its own as a good species, not subservient or subordinate to any 
other form that can be so described, no matter how apparently 
closely related. Forms of this kind may have (I say it ad- 
visedly : we have no proof to the contrary) approached each 
other through natural selection, without being off-sets in a direct 
line from a common parent. 
Again, why use the term “sub” at all, when a much simpler 
and less confusing arrangement may be employed in its stead. 
All naturalists are pretty well agreed that natural arrangements 
shall consist of orders, tribes, families, genera, species, and 
lastly, varieties. Beginning with ‘‘tribes” of any given order, 
we have—Tribe 1, consisting of certain families all agreeing in 
certain recognisable features or parts. Families which cannot 
be grouped under Tribe 1 would fall under Tribe 2, and so on 
numerically ad Zibitm, without one being subordinate to the 
other, which they really are not in nature. The same may be 
said of genera grouped into families, species into genera, &c. 
Dr. Hooker has done well in making varieties (or, as he terms 
them, ‘‘sub-species’”’?) of some plants which certainly have no 
other specific claim. As an instance, I may cite the three almost 
equally common forms of Asfidizm, all of which are included 
under A. aculeatum, Sw. This is decidedly a step in the right 
direction ; but should not the forms have retained the name of 
angulare in preference to aculeatum? The latter, I believe, 
claims priority, but the form described under angulare is de- 
cidedly the most highly developed, having stalked pinnules. 
Woodhay, Aug. 12 HENRY REEKS 
On Supersaturated Solutions 
My friend Mr. Rodwell was so good as to forward to me a 
copy of NATURE for the 4th inst., containing an account of 
some interesting experiments by Mr. Grenfell on the action of 
fatty bodies on supersaturated saline solutions. 
During the last two years I have made a large number ot 
experiments in order to ascertain the function of oils and fatty 
substances in determining the crystallisation of such solutions. 
The results of my inquiry are included in a paper, the abstract 
of which was read before the Royal Society on the evening of 
the 16th of June last, to which I beg leave to refer. 5 
