I40 



NA TURE 



{Dec. 9, 1886 



Many of the anchorages along the south-eastern coast of China 

 and the south-western coast of Formosa afiford excellent shelter 

 against north-east winds, but would prove to be much worse than 

 the open sea during a heavy southerly gale. If you observe a 

 northerly gale and a falling barometer, by far the surest signs of 

 an approaching typhoon, and appearances are rapidly getting 

 worse, then occasions may possibly occur when you may be under 

 the dire necessity of running southwards with the northerly gale, 

 against the rules laid down by meteorologists, and bring your 

 ship into a most dangerous position in front of the centre. But 

 you may happen to be better off there after gaining ample sea- 

 room, than in the snug anchorage, where your vessel would be 

 smashed against the rocks as soon as she began to drag her 

 anchors when the storm burst upon her from the south, although 

 the south-west storms experienced along the south eastern coast 

 of China during a typhoon that enters the mainland are as a 

 rule less violent or protracted than the preceding storm from 

 the north. 



Suppose that after leaving Hong Kong bound for a northern 

 port you were to ascertain the existence of a typhoon about to 

 cross your course in front of your vessel, and you experience, 

 say, a strong breeze from the west-north-west. If you do not 

 alter your course, you may, from the fact of its subsequently 

 appearing to be a hanging gale and seeing the mercury falling in 

 the barometer, draw the erroneous conclusion that you are on 

 the path of the centre of a typhoon coming down on you from 

 the east-north-east. In such a case it does not appear to be 

 advisable to .scud before the wind, it being decidedly wiser to 

 heave-to. Then if the gale is observed to begin to back towards 

 south-west, you maynm southwards and shape your course so as 

 to sail round the typhoon. Masters of steamers leaving Hong 

 Kong while the red drum is hoisted generally lose no time in 

 running southwards as soon as the typhoon is observed to have 

 taken a north-western course, and suffer very little delay in 

 consequence. 



Steamers bound for Shanghai are, while between Foochow 

 and Ningpo, liable to experience the northerly g.ales that precede 

 a typhoon of the second class travelling north-westward and 

 about to strike the coast in that locality. Not wishing to expose 

 their ships to the high cross seas round northern Formosa, the 

 masters generally take them into the nearest typhoon harbour 

 in order to wait till the centre has entered the mainland, and then 

 run northwards with the southerly gale. 



These few examples will be sufficient, the more so as the 

 further consideration of the subject would lead into details with 

 which the writer is not familiar, being possessed of no further 

 knowledge of n.avigation than the little that can be gleaned from 

 the inspection of log-books and from occasional conversations 

 with masters of vessels of many years' standing. The writer has 

 invariably found these gentlemen ready to recount their experi- 

 ences and to communicate any information, as soon as they found 

 that it was required for scientific purposes exclusively. The 

 m.aster of a vessel, after encountering a severe typhoon, has often 

 to undergo the vexation of seeing every manceuvre of his sub- 

 jected to the comments of those unaware of the hundreds of 

 things he has to take into consideration besides the law of storms, 

 and who were comfortably ensconced in their houses while he 

 was experiencing the typhoon with its fierce gusts, interrupted by 

 the, if possible, more ominous lulls, during which he cannot see 

 three ship's lengths before him, the mountainous waves in which 

 his good ship is but a "cock-boat," the loudest shouting in- 

 audible, drowned in the roar of the tempest, boats and everything 

 movable having been w ashed overboard, rudder gone, and per- 

 haps one of the masts thumping at her bottom, while the seas 

 threaten at every moment to swamp the ship. 



VI. The origin of a typhoon is not quite understood, but 

 appears to be connected with an abnorojally high temperature 

 and humidity in some place in comparison with the neighbour- 

 hood. Over such a place the hot air expands, ascends, and is 

 thereby cooled. But the heat liberated by the consequent con 

 densation of water-vapour retards the rate at which it cools on 

 rising in the atmosphere, and enables it to rise still further. 

 When the air has risen to a high level, it effects there an increase 

 of barometric pressure, in consequence of which the upper air is 

 set in motion out towards the circumference of the area in 

 question. Thus a fall in the barometer at the surface of the sea 

 in the middle of the hot and damp region is effected, and the 

 -surrounding air is impelled in towards the centre. The motions 

 inwards at the surface of the sea, and outwards at a high atmo- 

 spheric level, are, of course, contemporaneous, and one is assisted 



by the other. But air in motion is deflected towards the right 

 in the northern hemivphere, owing to the rotation of the earth, 

 except at or very near the equator ; whence typhoons do not exist 

 in that locality, for if the wind continues to blow into the 

 depression it is soon filled up. Giving to its deflection towards 

 the right, the wind is caused to move in a curved path in towards 

 the centre, and the centrifugal force, developed in the curvilinear 

 motion, deflects it still further from the straight line leading into 

 the centre. The friction between the wind and the greatly 

 disturbed sea-surface likewise retards the entrance of the air at 

 the sea-surface into the central parts of the depression. But the 

 air at a higher level in the atmosphere is subject to little friction, 

 and escapes therefore at a greater speed from the central high- 

 pressure area at that level. It is, therefore, apparent tha'; once a 

 cyclonal motion is started under circumstances favourable for its 

 continuation, it tends to increase and to spread outwards. 



There is, however, this important difference between a typhoon 

 and a tornado, that the latter is taller than it is broad, whereas 

 a typhoon perhaps does not reach above an altitude of four miles, 

 while its horizontal diameter may amount to upwards of a 

 thousand miles. Moreover, it is not at all likely that the centre 

 at a higher level lies vertically above the central calm at the 

 earth's surface, or even that the centres at different altitudes are 

 situated in a straight line. We are, therefore, scarcely entitled 

 to speak of an axis in a typhoon. 



The spirals described by the air panicles approaching the centre 

 in a typhoon .are known as logarithmic spirals, but unless a 

 typhoon is stationary, which is perhaps never the case in Nature, 

 new portions of air are constantly set in motion in front of the 

 centre and others left behind by the typhoon. 



As already remarked, the progressive motion of typhoons is 

 evidently caused by the wind prevailing, if not at the surface 

 of the earth, at any rate at a higher level. That the principal part 

 of the disturbance is situated high above the surface of the earth 

 is proved by the fact that the centres of typhoons pass across 

 mountains several thousand feet high, and also by the circum- 

 stance that the difference between the temperature at the Hong 

 Kong Observatory and at Victoria Peak is not perceptibly affected 

 by the approach of a typhoon, for we cannot very well assume 

 that the temperature of a vertical column of air is lower near 

 the centre than outside the cyclone. The mountains referred to 

 are situated on islands, and while crossing them the typhoon 

 derives its store of water-vapour from the surrounding sea, for 

 as soon as the centre has entered the coast, -and is on all sides 

 surrounded by dry land, it ceases to exist as a tropical storm, 

 and can only be traced in the registers through a slight fall in 

 the barometer, a freshening of the wind, perhaps amounting 

 to a moderate gale at stations crossed by the centre, and wet 

 weather. Inland in China the bull's eye of a typhoon does not 

 appear to be observed. 



.-Vs the wind blows more straight into the centre the nearer 

 the equator you are, it follows that more air enters the typhoon 

 from the southern semicircle than from the northern, and this 

 is one of the reasons why typhoons nearly always move in a 

 northerly direction. Moreover, the difference increases together 

 with the dimension of the typhoons, which explains why they 

 expand and accelerate their progressive motion at the same time. 



The foregoing observations contain the principal practical 

 results of investigations of abotit forty typhoons, continued during 

 a period of three years. The mariner into whose hands this 

 article may fall is advised to determine for himself the direction 

 in which the centre of a typhoon, which he is experiencing, is 

 travelling ; for although typhoons of the classes enumerated are 

 by far the most common, he never can be quite sure that he has 

 not to do with an exceptional case, and quite possibly a case 

 that is not found among the forty typhoons referred to above. 

 By the time that we shall be in possession of full .and trustworthy 

 investigations of a couple of hundred typhoons, we may expect 

 to have complete lists of the sub-classes of the four classes of 

 typhoons, and to be better acquainted w'ith cases of rare occur- 

 rence, for, after all, the typhoons are of a simpler construction 

 and their paths more regular than is the case with storms in 

 Europe. Typhoons are so violent near their centre that the 

 whole disturbance is evidently ruled thereby, whereas storms in 

 the North Atlantic and in Europe appear to be made up of a 

 lot of local eddies, some of which are by degrees detached from 

 the chief disturbance and form subsidiary depressions. The 

 writer has not been able to ascertain the existence of a subsidiary 

 depression in the China Seas during the last three years, and it 

 is therefore doubtful whether such ever occur. 



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