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From Gorruckpoor, in lat. 26° 45' N. long. 83° 22′ E. I learn by one letter that it blew a gale from the East on the night of the 5th and 6th June; strongly from the East during the 6th, and until the afternoon of the 7th, when it was NE., also blowing strongly; on the morning of the 8th it was NW. strong, and towards the afternoon it shifted to the East and moderated. The rain commenced at noon on the 6th and continued night and day till the afternoon of the 8th, when it ceased.
From Gorruckpoor I have also by the kindness of Mr. Vicars the following memorandum.
Gorruckpoor, 23rd September, 1839.
At the request of Mr. Bridgman, I send you an extract from my Meteorological Journal, it is a very unfortunate circumstance that I should have neglected to register the barometer and thermometer until the 7th of June, I however, noted the direction of the winds and the maximum of the Thermometer, which is better than nothing, and perhaps may answer your purpose; there was a storm from the East with rain on the 31st May.
8 28-788 77-5 78.5 28-777 79-577-8
928-902 80-7 80-228-940 84-0
(min. of Bar. 28.808) Estly. stg. rain all day. Easterly, strong, heavy rain till 4 P. M.
Easterly, strong, cloudy. Easterly. Variable. 10 28-961 81-081-028-800 82-8'83.0 Easterly, cloudy.
From Mirzapore lat. 25° 10' N. long. 85° 35' E. I am indebted to Mr. Stuart for the following memorandum of the weather, from 1st to
9th ditto, 10th ditto,
Blowing heavy from the East, showers, noon blowing very fresh and weather wild looking. A regular gale from the East with drizzling rain, noon gale increasing and more rain, evening stormy and wet.
Severe squalls through the night from the
Very wet morning, cleared up about nine.
My attention was drawn to this theory while endeavouring to trace some barometric curve, and some relation between it and the magnetic equator, and withal some law which might theoretically account for the paraboloidal course of the West Indian and American hurricanes, as shown by Mr. Redfield and Col. Reid; and the singular difference shown by the track of our Hurricane led me to suppose that it might perhaps move in the axis of the parabola? Mr. Ravenshaw's letter shortly afterwards gave much credit to these views, and subsequent facts serve to justify our asserting that for this time at least it has done so.
If we describe, as I have done on the Map No. II, a great parabola, one branch of which stretches towards Ceylon, and the other up to the valley of the Ganges towards Agra, the vortex being towards Arracan, and the axis in the line of the supposed track of the Hurricane; it will be found that the focus of such a parabola falls in about lat. 19° 36′ N. long. 88° 10′ E. which was about the centre of the Hurricane on the 4th. These sort of lines are of course arbitrary, but still the coincidence is novel and curious; whether we look upon the whirls of the Hurricane to have been produced by the mere dynamic action of the streams of air, like the eddies within the bends of a river flowing through a curved channel, or suppose that these vortices are Thermoelectric Phænomena, produced by the sudden transfer of great volumes of the caloric and moisture of the stream of air from the warm equatorial regions to the colder ones toward and beyond the tropics. The remarks on the warmth of the weather in the logs, and the thermometrical
* It may be worth remarking that while this hurricane seems to have travelled from East to West or nearly parallel to the direction of the Magnetic Equator as laid down by Biot, those of the West Indies seem for the most part to come from the South Eastward, which is also there the direction of the plane of the Magnetic Equator. The "( Raleigh's" Hurricane in the China Seas seems too to have travelled in this direction.
register, with the peculiar state of the atmosphere so well described in the remarks of Captain Paterson, of the H. C. S. Amherst-and her track from Akyab we must remember was almost in the direction of the path of the hurricane till it overtook her at the Sand Heads-are well worth considering.
These are but vague theories, it will be said, but it will not be forgotten that theories on a new subject, like torches in exploring dark caverns often lead us to the passage we seek; though not by the road we expected. "We have only to be ready to lay them aside when they have served our turn," ,"* and if I venture to introduce this one here it is to point attention to the importance of obtaining electric observations if possible.
The slow rate at which the vortex appears to have travelled also seems to show, as before remarked, that it was, as it were, pent up between the great stream of air blowing along the Arracan range and the Coromandel Hills. We see analogous instances to this in the small bays at the sides of rivers, where while there is one part of the stream turning round the shores of it and another flowing from point to point, we see the eddies are from time to time found almost stationary about the middle of the bay.t
I wish to be understood here however as suggesting probable comparisons rather than advancing a theory.
Col. Reid and Mr. Redfield give from ten to thirty miles per hour for the rates at which the centres of their different vortices have probably travelled onwards. If our centres are correctly laid down ; and I think there is good evidence that at least those of the 4th and 5th are so; it appears that from the 3rd to the 4th the Hurricane travelled onwards only about 100 miles, or say 4-16 per hour, and from the 4th to the 5th about 70 or 83 miles per hour. This again is conformable to what we observe in the bends of a stream where the eddies seem to start from some point, and move onwards with more rapidity in the first part of their course than latterly. Should future experience confirm this instance of the slow progress of our Hurricane, it will become an important element in any calculation to be made by the seaman for avoiding their violence.
* Sir John Herschel.
In the rivers of India banks are often formed at these points, which ending by choking the stream as the river becomes lower, changes its channel in succeeding years.
Practical Remarks and Deductions.
I have quoted at p. 563 an opinion expressed in my hearing, that it was thought by the individual that "they would not make much of it." Few I think who have perused the preceding pages, will be inclined to repeat this, but still as the plain man and the practical seaman may not so readily arrive at all the conclusions to be drawn from the knowledge we have collected of this single tempest, I have been induced to sum them up here.
My original intention was to delay doing this, and even the publication of this memoir, until I could collect also what was to be gleaned from the records now existing of our former gales and hurricanes, and then accompany the whole with practical deductions; but it was suggested to me by Professor O'Shaughnessy, that by the delay which this would occasion, we should loose the opportunity of exciting public attention to the subject before the approach of the autumnal gales, and moreover, that even by publishing our knowledge in this yet imperfect state, we might nevertheless, possibly, avert mischief. This I thought sound counsel, and therefore propose to make our former Indian tempests the subject of a future memoir.
It will then be recollected that what is here said is merely the amount of our present knowledge, and that what is said is rather meant as a suggestion than as a rule. I shall however distinctly state the grounds from which the various inferences are drawn, and it will be for every man to exercise his own judgment thereupon; I shall also acknowledge when I borrow from Colonel Reid, or other writers.
Clearly to comprehend this theory of gales and hurricanes, let us begin with the words. As I have elsewhere said, the words are not to be used so much with relation to the force of the wind in a storm, as to its motion.
A storm, or tempest, may mean either a Gale or Hurricane, but it always means a storm of wind, and not, as frequently used by landsmen, one of thunder and lightning only; unless so expressed.
A gale means a storm of wind, the direction of which is tolerably steady for a long time, sometimes not only for days but for weeks.
A hurricane means a turning storm of wind blowing with great violence, and shifting more or less suddenly, so as to blow half or entirely round the compass in a few hours.
With this explanation of our words we shall better understand the things treated of.
The present state of our knowledge seems to show that for the West Indies, Bay of Bengal, and China Sea, the wind in a hurricane
has two motions, the one a turning or veering round upon a centre, and the other a straight or curved motion forwards, so that it is both turning round and rolling forward at the same time. It appears also that it turns, when it occurs on the North side of the Equator from the East, or the right hand, by the North, towards the West; or contrary to the hands of a watch; and in the Southern hemisphere, that its motion is the contrary way, or with the hands of a watch. The foregoing memoir with the charts and diagrams shew that this rule holds good at least for our storm of June last; and that the wind was really blowing in great circles in a direction as described; i. e. against that of the hands of a watch. We assume then for the present, that the hurricanes in the Bay of Bengal always follow this law. We do not yet positively know that such is the case, but it is the most probable opinion.
If we describe on a piece of paper a few concentric circles, like those in the diagrams, and marking a little compass with its fleur de lis to the North in the middle make four arrows at the top, bottom, and two sides, writing against them as in the diagram, East-wind, Northwind, West-wind and South-wind, and then cut this out with scissors, we shall have what is called a Hurricane-circle or Hurricane-card.
The use of this is to lay it down upon any part of a chart. We may also cut out a little spindle-shaped piece to represent our ship, and place this in that quarter of the card at which the wind is found.
The card may be supposed to represent a circle of fifty or of five hundred miles in diameter, as we please; and one which would fill up the head of the Bay of Bengal would show, on our map No. II, the wind South on the Arracan coast, East at the Sand-Heads, North on the coast of Coromandel, and West across the Bay.
We have now to judge of three important points, What is the track of the hurricane if it is to be one? In what direction does it bear from us now? How far are we from its centre?
We do not yet know what is the usual track of our Indian hurricanes. We know from Col. Reid's and Mr. Redfield's researches that those of the West Indies begin about the Leeward Islands, travel to the WNW. and then round the shores of the Gulf of Mexico, and following the
Gulf Stream, are lost in the Atlantic between the Bermudas and Halifax; and they have investigated a sufficient number to show that this may be taken as a general rule. Those also of the Mauritius seem to come from the Eastward. All we yet know positively here is the course of this single tempest; and hence the great necessity of further observation and research, to which I shall perhaps farther allude. We may however, in the absence of better knowledge, take it as