102 
NATURE 
| Fane 8, 1871 

There is nothing more trying for a master’s patience—and I 
speak from experience—than this persistent and short-sighted 
adherence to what has gone before, just as if the world (the agri- 
cultural world particularly) had to jog on to the end of time in 
the self-same fashion. 
Whatever united action, therefore, may be taken by our leaders 
in science for bringing about a more healthy feeling on this sub- 
ject, for scattering science and a love for it in every household, 
depend upon it the readiest and surest way will be to urge on 
Government to introduce, nay, force, the subject freely and uni- 
yersally into all schools, so that it may grow up with the rising 
generation, and become a part of their very existence, The task 
is Herculean, no doubt. An enormous amount of prejudice will 
have to be overcome, but 
Sedit, qui timuit ne non succederet ; esto: 
Quid? qui pervenit fecitne viriliter ? 
Lectures on science will thus be not merely listened to as now, 
but understood and appreciated. Superstition, the child of 
Ignorance, will be dispelled, and a nation of reasoning and think- 
ing men and women inaugurated as the glorious and inevitable 
consequence. THOMAS FAWCETT 
Blencowe School 
Preponderance of West Winds 
I HOPE you will publish this reply to Mr. Laughton’s letter in 
Nature of May 4, on the Prevalence of West Winds. 
He maintains from statistical evidence that west winds occupy 
a greater portion of the earth’s surface than east winds ; that 
their force is greater ; and that in the upper regions of the atmo- 
sphere the preponderance of west winds is still more decided 
than at the earth’s surface ; so that on the whole the atmosphere 
moves round the earth from west to east. 
It is in my opinion certain that this is on the whole proved. 
IT do not question Mr. Laughton’s facts but his inferences from 
them. He thinks this rotation points to some force acting from 
without—some cosmical cause of a nature quite unlike the sun’s 
leat. I maintain, on the contrary, that all the phenomena of 
the great atmospheric currents, of which the trade-winds are a 
part, are to be accounted for by the heat of the sun as the 
motive power, combined with the rotation of the earth as a 
modifying influence. 
In discussing the question of whether the phenomena point to 
such a cause as that suggested by Mr. Laughton, the motion of 
the upper strata of the aimosphere is quite unimportant. It is 
only the currents at the surface of the earth that can in however 
infinitesimal a degree increase or diminish the velocity of the earth’s 
rotation ; and if the circulation of the atmosphere is due to the 
sun’s heat as its motive power, it cannot have the slightest 
effect on the earth’s rotation; while if it is due to any mechanical 
force acting from without, as Mr. Laughton thinks—if the Carte- 
sian theory is true, and the circulation of our atmosphere is part 
of a cosmical vortex—the earth’s rotation must be accelerated 
by its friction. This follows from the simplest dynamical prin- 
ciples. It is true that the acceleration which could be produced 
in such a way would at the greatest be far too small for us to 
detect ; but it is quite possible for us to ascertain whether or not 
the currents of air that sweep over the surface of the earth are 
by their united action capable of affecting its rotation ; or, to 
state the problem more definitely, whether or not the elfect of | 
west winds in accelerating the rotation is balanced by the effect 
of east winds in retarding it. I maintain that such evidence as 
we have tends to the conclusion that the effects of the two are 
so balanced. 
The separate effect of any wind covering a given area on the 
earth’s rotation = the east and west component of its force x the 
radius of the parallel of latitude. The latter factor gives 
leverage. An cast wind near the equator has more effect in 
retarding the rotation of the earth than a west wind of equal 
extent and force at a higher latitude has in accelerating it, just 
as a weight at the end of the long arm of a lever out- 
weighs an equal weight at the end of the shortarm. Now, the 
east winds, under the name of trade-winds, are chiefly to be 
found in the lower latitudes, and for the reason just given they 
are able to balance the west winds, which are certainly more 
forcible, and according to Mr. Laughton, occupy a greater area, 
but being at higher latitudes act at a disadvantage. Ifit can be 
shown—and the facts certainly point to it—that the total me- 
chanical effect of the winds is not such as to produce any effect 

on the earth’s rotation, this goes very far to prove that they have 
no motive power except the sun’s heat. 
But how is the motion of the upper strata of the atmosphere 
from west to east to be accounted for? The answer to this will 
involve the entire theory of the great currents of atmospheric 
circulation, There is always a current of air towards a heated 
place along the earth’s surface, like the draft towards a fire, and 
a compensating current of air away from it in the upper regions 
of the atmosphere. The equatorial latitudes being the hottest, 
there are currents to them from the higher latitudes, which bring 
with them the smaller velocity due to the rotation of the higher 
latitudes, and thus move less rapidly than the earth in those lower 
latitudes to which they flow. Moving with a less velocity than 
the earth is the same as moving from the east, and thus are the 
trade-winds constituted ; they are from north-east in the northern 
hemisphere and from south-east in the southern. This is gene- 
rally understood and believed ; what follows is less generally 
understood, though I claim no originality for it. 
The air rises up over the equatorial regions like a column of 
smoke over a fire, and flows off towards the poles, Coming from 
the latitudes where the velocity of the earth’s rotation is greatest, 
it carries that greater velocity with it, and spends the energy of 
its motion in the form of the west winds of the higher latitudes, 
The reason, then, that the upper strata of the atmosphere (in all 
latitudes except on the equator) have a motion round the earth 
from west to east, is simply that they are at the same time moving 
from latitudes where the velocity of the earth's rotation is greater 
to latitudes where it is less, JosEpH JOHN MurRPHY 
Remarkable Sun-spots 
THE accompanying sketch shows in a rough way the umbrze 
and a small portion of the penumbra of a sun spot that I ob- 
served on the 6th and 7th of this month, and which was made 
remarkable by the presence of a reddish-brown object like a 
cloud, that seemed to hang over the nucleus of the principal 
umbra, apparently dividing it in two. Could this object be seen 
without the intervention of the dark glass, it would doubtless 
show a bright red instead of a reddish-brown colour ; and from 
its fog-like aspect, though it was well defined in outline and 
acuminated at both ends, the impression was inevitable that it 
hung at a certain altitude above the spot. However, it evi- 



dently had no motion distinct from the latter, as on the 7th it 
occupied the same position as on the day before, but it was 
much reduced in size. On the Sth it was seen no longer, and 
the nucleus was now in one, seeming to show pretty clearly that 
its previous apparent division in two was really caused by the in- 
tervention of the brown cloud suspended over it, and that the 
phenomenon did not consist of two distinct neuclei with the brown 
object lying between them, I am not aware that anything like 
this was observed before, J. BIRMINGHAM 
Millbrook, Tuam, May 18 
ee 
