Yune 23, 1870] 
NATURE 1ST 
Mk. MELDRUM ON THE ORIGIN OF STORMS 1N 
THE BAY OF BENGAL* 
THE writer commenced by observing that in various papers 
published during the last ten years, he had_ stated, as the 
result of an examination of a large body of observations, that 
the tropical cyclones of the Indian Ocean, south of the Equator, 
originated between two contrary streams of air, viz., the N.W. 
monsoon and the S.E. trade-wind ; and, in a paper read on the 
1oth of November last, he remarked that what had been found 
to hold good in that part of the ocean might be found to do so 
generally. As the observations collected by the Society only 
referred to the Indian Ocean, he could not directly test the 
matter with regard to the cyclones of other parts of the world. 
But cyclones also occurred in the Indian Ocean, north of the 
Equator, and as the Society possessed observations which had 
been taken there, he proposed to examine the records with a 
view of ascertaining whether these cyclones were formed, as he 
believed those south of the Equator were, between two 
oppositely directed currents of air which had pre-existed. It 
was to that point alone that he wished to direct attention at 
present. How the barometric depression in the heart of a 
cyclone was formed, whether owing to an ascending current, to 
condensation of vapour, or to other causes, why the air moved 
more or less round a central area in a particular direction, and 
why the cyclone had a progressive movement, were subjects 
upon which he would not then touch ; for the question of the 
existence or non-existence of opposite winds, previously to the 
formation of the cyclone, had, in his opinion, an important 
bearing upon all the others, and should therefore be taken 
up first. 
The cyclones of the Indian Ocean, south of the Equator, as 
was well known, took place during six months of the year, viz., 
November to May. During that period the N.W. monsoon 
prevailed from near the Equator to 10° or 15° S., sometimes 
stretching as far south as the tropic. Still farther south the 
S.E. trade-wind prevailed. The line or belt separating the two 
winds often ran obliquely across the ocean from 18° S., near 
Madagascar, towards the Straits of Sunda. It was in that belt 
of comparatively low barometer, calms, and variables, that the 
tropical cyclones of the Indian Ocean, south of the Equator, were 
formed, The N.W. monsoon was a continuation of the N.E. 
trade-wind of the northern hem'sphere. This might be seen on 
almost any day from November to April or May, by laying down 
-the directions of the wind at a sufficient number of points ; and 
the daily charts which had been prepared for various periods 
showed it very clearly. On examining those for February, 
1861, for example, which had lately been lithographed, it would 
be seen that the N.E. trade-wind prevailed over the Bay of 
Bengal and the Arabian Sea, that as it approached the Equator 
_ it became more northerly, and after crossing the Equator into 
the southern hemisphere it became the N.W. monsoon. The 
southern limits of the N.W. monsoon, and the northern limits 
_ of the S.E. trade, or, in other words, the position of the belt of 
_ variables between them, moved backwards and forwards accor- 
ding to the season. It was farthest S. when the southern 
~ hemisphere was warmest. As the temperature decreased, to- 
wards the end of March, this belt retreated northwards with the 
sun, came up to the Equator, and crossed it into the northern 
hemisphere. In whatever part, N. or S. of the Equator, 
the belt of calms existed, the prevailing winds on either side of 
- it were from opposite directions. When it was S. of the 
_ Equator, the prevailing wind to the southward of it was from 
the S.E. or E. (the S.E. trade), and to the northward of 
it from N.W. or W. (the N.W. monsoon.) The latter ex- 
- tended at least as far N. as the Equator, and the N.E. trade, 
~ of which it was the continuation, prevailed over the Bay of 
_ Bengal. ‘The former at the same time prevailed as far south as 
the parallel of 30° or go° S. When the belt of calms was N. 
of the Equator, the prevailing wind to the S. of it was from 
: S.W. or West, and to the N. of it from N.E. or E. The 
_ former was the S.W. monsocn, and the latter the N.E. trade- 
wind. In July and August, when the belt was far N., the 
__§.W. monsoon prevailed over the whole of the Bay of Bengal, 
and was a continuation of the S.E. trade-wind, just as the 
_N.W. monsoon in February and March was a continuation of 
_ the N.E. trade-wind.. The belt of calms followed the sun, 
moving from one tropic to the other, and often passing them. 
_ Hence, when it was at its northernmost limit, the S.W. mon- 
i * Paper read before the Meteorological Society of Mauritius, March 24, 1870, 
soon swept over the Bay of Bengal, and when at its southern- 
most limit, the N.E. trade-wind did so. But at certain seasons, 
when the belt of calms stretched across the Bay, the S.W. 
monsoon blew over one part of it and the N.E. trade over the 
other. 
As, then, observation had shown that the tropical cyclones of 
the Indian Ocean, south of the Equator, were formed in the 
belt of calms between the N.W. monsoon and the S.E. trade- 
wind, and nowhere else, there was at least a presumption that 
the cyclones of the Bay of Bengal were also formed in that belt, 
at those seasons when it stretched across the Bay, and separated 
the N.E. trade wind from the S.W. monsoon; and this presump- 
tion was strengthened by the fact that most, if not ail, of the 
cyclones that occurred there, did so at the change of the mon- 
soons ; that is, when two contrary winds prevailed in the Bay, and 
were more or less in conflict. 
These general considerations rendered it possible, if not pro- 
bable, that the cyclones of the Bay of Bengal were formed 
between two contrary and pre-existing winds. But that was 
not sufficient. It was necessary to bring the matter to the test 
of facts ; and this could only be done by examining the observa- 
tions taken in particular storms. He weuld begin with the de- 
structive storm which visited Calcutta on the 5th October, 1864. 
On the 12th September in that year, the ship Fzress Addey, 
Capt. Roddock, in 19° 08’ N. and 88° 55’ E., had a fresh breeze 
from W.S.W. and S.W., and she carried that wind to 4° 44’ N. 
and 92° 38’ FE. on the 21st. The Victorza Nyanza, Capt. A. 
J. Reed, had a strong wind from S.W. on the 21st. Sept., in 
18° 17’ N., and 87° 46’ E., and she carried that wind to 0° 45’ 
S. and 91° 02’ E. on the 25th. The French barque Leoniue, 
Capt. Martin, outward bound, aprroached the Equator with the 
S.E. trade-wind, which gradually veered to S. and S.S.W., 
and from 1° 59’ N. and 84 05’ E. on the 6th, to 19° 29’ N. and 
88° 27' E. on the 13th Sept., she had fresh and strong winds 
from the S.W. Moreover, he had prepared a chart for the 21st 
September, which showed that on that day eleven vessels, 
from the Equator to 20° N., in the Bay of Bengal, had the 
wind from W.S.W. and S.W., in moderate and fresh breezes. 
These observations proved that up to that date the S.W. mon- 
soon prevailed in the Bay. But a change was at hand. On 
the 26th September, the wind in the northern part of the 
Bay was light from the northward, and in the southern part 
moderate from westward. On the 29th September there 
was a strong breeze blowing from the W.S.W., with squally 
rainy weather from near the Equator to at least 10° N., whilst in 
the northern part of the Bay the wind was light from the N. On 
the 2nd Oct. there were signs of a cyclone. To the S.W. of 
the Nicobars a strong breeze was blowing from the W.S.W., 
with squally rainy weather. In the Gulf of Martaban there was 
a gale from the S.E., with much rain and lightning. To the 
S.E. of Coringa the wind was increasing from N.E., with thunder 
and lightning. On the 3rd and 4th there was strong evidence of 
the existence of two contrary winds, the one from N.E. and the 
other from S.W., with a cyclone between them; but the S.W. 
wind was apparently overcoming the other. On the 5th, when 
the storm was at Calcutta, the S.W. wind had established itself 
over the greater part of the Bay. But this was only a temporary 
victory, for by the 8th the N.E. wind was blowing fresh over the 
northern portion of the Bay. The S.W. wind, however, still 
prevailed farther south. By noon on the 15th the N.E. wind 
prevailed over the whole Bay. 
He had not been able to examine the subject farther, but would 
return to itat next meeting. Inthe meantime, he thought that 
the evidence adduced went to show that the storm originated 
in the belt of calms between the N.E. trade and the S.W. 
monsoon. 
CHEMISTRY 
Specific Gravities of Aqueous Solutions 
In Gerlach’s Sammlung der specifischen Gewichte wisseriger 
Lésungen is a large amount of information which will prove of 
great use to manufacturers and others who have to deal with 
aqueous solutions of acids, alkalies, and salts. 
The first table consists of nine columns marked with letters. 
In column A are placed the formula and combining weights, 
according to the old notation, of the bodies dissolved, both inthe 
anhydrous and hydrated condition, Column B contains the 
weight of the dissolved body in the hydrated condition, or with 
