288 
NATURE 
[Fuly 29, 1886 
identity with that of the earth’s rotation, solar tidal friction will 
further reduce the earth’s angular velocity, the tidal reaction on 
the moon will be reversed, and the moon’s orbital velocity will 
increase, and her distance fromthe earth will diminish. But 
since the moon’s mass is very large, the moon must recede to an 
enormous distance from the earth, before this reversal will take 
place. Now the satellites of Mars are very small, and therefore 
they need only to recede a short distance from the planet before 
the reversal of tidal friction.” 
No one can have any datum for saying that the Martian satel- 
lite must have fallen into the planet ‘‘long ere this,” but Mr. 
Nolan shows that the satellite is now near the end of its 
history. 
I do not think that Sir William Thomson made any allowance 
for solar tidal friction in estimating the ultimate distance of the 
moon. Both he and I only cared to obtain the result in round 
numbers. 
I should be very much obliged to Mr. Nolan if he would give a 
reference to the proof of the theorem, that two heavenly bodies 
cannot revolve about their centre of inertia, as parts of a rigid 
body with their surfaces nearly in contact, unless one is smaller 
and denser than the other by a certain amount. 
July 15 G, H. Darwin 
Peripatus in Demerara 
CONSIDERING the great antiquity and importance of Peripa/us 
it seems desirable to make a public notification of the fact that I 
have found a species, apparently Perifatus Edwardsi, in the 
Demerara division of British Guiana. Four specimens were 
obtained by me, but three of them, owing to some unknown 
cause, became considerably damaged and _ practically useless. 
The fourth specimen, which was found by me nearly a month 
ago, is still alive and evidently in good health. It is, when in 
progression, about 34 inches in length, but it often elongates it- 
self considerably more and at other times becomes nearly coiled 
into a thick lump. It possesses thirty-one pairs of feet, the last 
three of which it rarely puts to the ground except when it goes 
backwards for short distances. Several other pairs at intervals 
along the body are carried off the ground in the same manner. 
It seems distinctly restless under the influence of light, appear- 
ing comfortable only when it retreats into some moist and 
darkened corner. When handled, it frequently discharges its 
viscid secretion, but as frequently neglects to do it when 
handled for the first time after a long interval, but more 
especially when touched or taken up for three or four times in 
rapid succession. It has been kept in an old sardine tin with 
small pieces of decayed wood, which were taken from the stump 
in which it was found, and the wood is kept in a moist condi- 
tion. The locality from which it was obtained was the Hoorubea 
Creek, about twenty miles from Georgetown, on the east coast 
of the Demerara River, close to the meeting-point of an ex- 
tensive forest and a water savannah. The four specimens were 
obtained in the same locality ; and, though I have sought for 
them continually in other places, up to the present I have been 
unable to find others. From the long period of time during 
which this specimen has survived in confinement, I think there 
will be no difficulty, when I have obtained a large number of 
specimens, in sending them alive to England to Prof. Moseley 
and others. Unfortunately I have no possible access here to 
any literature on the group. I do not think it is generally 
known, but Mr. Im Thurn has once previously found specimens 
of Peripatus in the Essequebo division of British Guiana. His 
specimens were, however, very small ones. 
British Guiana Museum JoHN J. QUELCH 
Upper Wind-Currents over the Bay of Bengal in March, 
and Malaysia in April and May 
IN my last letter to NATURE, yol. xxxiii. p. 460, on the 
subject of upper winds, I described the circulation of the Indian 
Ocean from the equator, where the north-west wind changes 
into the north-east monsoon, as far north as Ceylon, in the 
month of February. From there, about the beginning of March, 
I took a section of the weather, as nearly straight as practicable, 
from Colombo, through Calcutta, and 400 miles due north to 
Darjeeling. 
The general weather system at that season is very simple. A 
belt of high pressure lies across the Bay of Bengal, from about 
Madras, to the southern limits of Burmah. ‘The north-east 
monsoon blows to the south of this, towards the low pressure 
below the equator; the belt, of course, covers a calm area; 
while to the north a south-west wind blows towards a low pres- 
sure somewhere beyond the Himalayas. 
The upper currents over the north-east monsoon always blew 
from some more easterly point than the surface-wind ; the cloud- 
less sky over Madras prevented any observations ; north of this 
the higher clouds always came from some point more northerly 
than the south-west wind below. The lofty range of the 
Himalayas seemed to make no difference ; at Sendukphu I suc- 
ceeded in getting a photograph of acumulo-form cloud trailing 
from the summit of Kanching Junga (29,000 feet) well from the 
west-north-west, while a south-west wind was driving up mist 
from the plains. The existence of cumulus at so high a level 
has, I think, been denied by some meteorologists. 
All these observations are in complete accordance with the 
normal circulation of the northern hemisphere ; but the character 
of south-west monsoons deserves notice. The term south-west 
monsoon is unfortunately used for two different stages of the same 
weather sequence, and much confusion comes thereby. Maury and 
others think only of the direction of the wind ; common parlance 
all over the East talks of the monsoon as of a rainy season which 
sets in suddenly, long after south-west winds have been blowing 
for weeks or months previously. 
The facts of the case are these :—As early as January a light 
south-west wind commences in the north of the Bay of Bengal, 
first only as a sea breeze; later, when we encountered it, as a 
light continuous wind. Nothing can be more lovely than the 
weather then; bright blue sky, scarcely a light cloud, with a 
warm gentle wind; the monsoon, unlike March, begins like a 
lamb and goes out like a lion. As the season goes on an area 
of low pressure, which has been gradually forming over Northern 
Bengal, becomes more pronounced, and the south-west wind 
gradually works further and further to the southwards below 
Ceylon. Then, sometimes in June, a sudden total change comes 
over the weather, while the only alteration the isobars show is a 
slight motion of the lowest pressure towards the North-west 
Provinces of India. A sudden burst of rain and thunder breaks 
over Ceylon, and then the bad weather works slowly north- 
wards. ‘This is the commencement of the south-west monsoon 
in common talk. Everyone will tell you how many days it 
takes to work up to Bombay on one side and to Calcutta, by 
way of Burmah and Assam, on the other. Madras escapes for 
| the present, only to be deluged in November by the north-east 
monsoon. So we get the curious sequence that the wind works 
downwards, the rain upwards ; and also the fact that the greatest 
and most sudden change in the year is associated with no 
striking change in the distribution of pressure. The Indian 
meteorologists are of opinion that this sudden change in the 
character of the same wind is due to a sudden irruption of air, 
highly charged with vapour from the neighbourhood of the 
equatorial doldrums, but that the south-east trade is not linked 
with the south-west monsoon in a continuous current, except 
occasionally and temporarily. Would it not be of the highest 
interest and importance to discover whether this sudden change 
of weather is associated with any change in the relation of the 
upper and lower winds? In my letter to NATURE (vol. xxxiii. 
p- 460) I showed that over the south-west monsoon of the 
Gulf of Guinea the upper currents were those of the southern 
hemisphere, and that the south-east trade there seemed to grow 
gradually into a south-west wind as it crossed the line. If in 
Ceylon and India the higher clouds continue to come, as we found 
them, from west or north-west after the burst of the south-west 
monsoon, there must be a doldrum between it and the south-east 
trade ; but if the upper currents turn towards south or south-east 
after the burst, then undoubtedly the south-east trade has in- 
vaded the northern hemisphere. The latter is of course the old 
theory of the monsoon ; and perhaps another test may be ap- 
plied to the solution of these alternatives. If the south-east 
trade blows into a doldrum, there must be a belt of high pressure 
between Ceylon and the equator to give gradients for south-west 
winds. Has this ever been found? I do not think that calm 
alone is sufficient to be called a ‘‘doldrum.” During the north- 
west monsoon, which is unquestionably the north-east monsoon 
drawn across the line, the direction of the wind changes gradu- 
ally, but the velocity is often less just on the equator than on 
either side. I made some special inquiries on this point. 
In the Philippines, China, and Japan the upper winds over 
the south-west monsoon follow the normal course of the northern 
hemisphere ; but there jis no burst of the monsoon in those 
countries. 
