Narrative of the Circumnavigation of the Globe by the Austrian Frigate Novara Volume Iii Part 26

Signature of emigrant, __________

APPENDIX D. (pp. 539-548).

DESCRIPTION OF THE TYPHOON ENCOUNTERED IN THE CHINESE SEAS, BY H.I.R.M.'s FRIGATE NOVARA, ON THE 18TH AND 19TH AUGUST, 1858.

The path of the typhoon has been deduced from comparison with the readings of the barometer, with which it corresponds pretty accurately, if due allowance be made for the fact, that in determining it the various directions in which the line of centres runs must be calculated on the supposition that the orbit of the cyclone is circular, which it is not in reality, since at any considerable distance from the centre it must be elliptical. Hence it is apparent that the rate of velocity of the cyclone in advancing along its path follows no fixed law, whereas some such regularity undoubtedly exists among the ma.s.ses of air encountered by the cyclone. Hence too the errors thus made in specifying the direction of the wind become of considerable importance in this connection, more especially in the event of the place of observation being at any distance from the centre, or that the path of the cyclone forms a sharp angle when wheeling round. Moreover, as actually experienced, the path of the typhoon would lie more near the line of the points of observation than a sketch founded upon such observations would indicate, and than a general comparison of the paths of cyclones founded upon the theory of their gyratory motion would substantiate, except in those cases where the observer has been directly in the path of the cyclone.

In our case the absolute distances, as specified in the annexed table (see p. 490) of fifteen different stations taken during the three days during which the cyclone and its premonitory and subsequent symptoms lasted, are only a.s.sumed, because simultaneous observations of the varying directions of the wind could not be taken at various points of the course of the cyclone, and in so far may be inaccurate, although the relative distances might possibly be tolerably correct.

The observations as to the direction of the wind at noon of the 18th August and at the ensuing midnight, give results contradictory to the theory, since the wind in both cases is almost the same as would at midnight of the 19th indicate a central point, falling actually behind that portion of the path of the line of centres already traversed on the 18th. Upon this showing the direction of the wind at 6 P.M. of the 18th may be a.s.sumed as that of the centre of the cyclone. In fact, the path of the cyclone at this point lay parallel with the course the s.h.i.+p was holding, whence only trifling variations would be observable in the direction of the wind at those periods. Besides, the cyclone was at that time approaching the vertex of its...o...b..t, in doing which it encountered the large and tolerably lofty island of Okinawa-Sima of the Loo-Choo group, which must have resulted in a certain expenditure of the force causing the gyratory movement of the cyclone. In a.n.a.lyzing the path of the cyclone, account must also be taken of the winds that prevailed from the 17th August up to midnight, although these are to be considered, with respect to the cyclone proper, only in so far as they were winds that had been altered in direction at the origin of the typhoon in conformity with the laws of cyclones, which by no means imply in all cases a perfect gyration. However, as these winds are varied in direction by the same causes which are in full activity in the case of the cyclones, such variations must follow the same laws, and the lines of centres which present themselves with reference to these as parts of a circular orbit, naturally lie in the same direction as that of the cyclone at its origin.

As early as the 13th August a marked alteration in the temperature of the air had been perceptible at Shanghai; the thermometer fell from between 86 and 95 Fahr. to between 73.4 and 78.8 Fahr.: easterly breezes set in, and the barometer rose in a remarkable manner for that lat.i.tude and season. On the 17th the weather was still fine, but the sun set red and fiery behind a dense ma.s.s of clouds.

The morning of the 18th broke with continued fine weather; but c.u.mulous clouds were ma.s.sed on the sky, and looked black and threatening to the N.E. By 8 A.M. the wind and sea had both risen materially. By 3 P.M. the roll of the sea was from N. by E., the sky became still more cloudy, and the clouds began to descend; banks of clouds in the direction of the central point. At midnight between the 18th and 19th altered course to W.

by S., in order to run out of the cyclone by reaching its southern edge.

On the 19th at 8 A.M. a heavy sea from the northward, the sky a dense ma.s.s of clouds with very limited horizon; the whole aspect of the heavens a grey misty wrack of clouds, gradually falling lower and lower,--only in the direction of the central point was there visible a gloomy, leaden-coloured segment of clear horizon. From 4 P.M. to 8 P.M. the clouds completely enveloped us, so that it was barely possible to descry an object a cable's length from the s.h.i.+p; constant gusts of wind with fine rain or sea-spray; very heavy sea from the west, but the waves fairly decapitated by the wind as fast as they rose. By 11 P.M. a few dark clouds became visible in the S.S.E., and the horizon began to widen again.

20th. The sky still covered; in the west, white parallel bands of clouds, forming segments of circles: the masts and rigging covered with a crust of evaporated salt.

17th August.

Hours Mean Direction Strength from pressure of wind. of wind midnight of 0 to 10.

to atmosphere.

midnight.

1 29.908 S.E. 3/4 E. 3.5 2 .912 S.E. by E. 1/4 E. 3.5 3 .915 S.E. by E. 1/4 E. 3.5 4 .917 S.E. by E. 1/2 E. 2.5 5 .914 S.E. by E. 1/4 E. 2.5 6 .913 E.S.E. 2.5 7 .909 S.E. by E. 3/4 E. 2.5 8 .899 E.S.E. 3.

9 .886 S.E. by E. 1/2 E. 3.

10 .878 E. by S. 1/4 S. 3.

11 .869 E. 3/4 S. 3.

12M. .860 E. 1/4 S. 3.

1 .852 E. 1/2 S. 3.5 2 .853 E. 1/2 S. 3.5 3 .848 E. 3.2 4 .834 E. 1/2 N. 4.

5 .817 E.N.E. 4.

6 29.808 E.N.E. 4.

7 .810 N.E. by E. 1/4 E. 4.

8 .812 N.E. by E. 1/4 E. 3.5 9 .812 N.E. by E. 3.5 10 .806 N.E. by E. 1/2 E. 3.5 11 .795 E.N.E. 3.5 12 .784 E.N.E. 3.5

18th August.

1 29.779 E. by N. 3.5 2 .771 E. by N. 3.2 3 .762 E. by N. 3.2 4 .758 E. by N. 3.2 5 .751 E. by N. 3.5 6 .740 N.E. by E. 1/2 E. 3.5 7 .721 N.E. by E. 4.

8 .696 N.E. by E. 4.5 9 29.666 N.E. by E. 5.

10 .640 N.E. 5.2 11 .612 N.E. 1/2 N. 5.7 12M. .581 N.E. by N. 6.5 1 .548 N.E. by N. 1/2 N. 5.

2 .526 N.E. by N. 6.5 3 .50 N. 7.5 4 .482 N. by E. 7.

5 .459 N.E. by N. 7.5 6 .435 N.E. by N. 8.

7 .421 N.E. by N. 8.

8 .411 N.E. by N. 8.

9 .408 N.E. by N. 8.

10 .405 N.E. 3/4 N. 8.5 11 .401 N.E. 1/2 N. 8.7 12 .375 N.E. 1/2 N. 8.7

19th August.

1 29.306 N.E. by N. 5.7 2 .319 N. by E. 8.

3 .335 N. by E. 7.

4 .351 N. 7.5 5 .364 N. 1/2 E. 7.2 6 .376 N. 7.2 7 .383 N. by W. 6.5 8 .376 N. by W. 1/2 W. 7.2 9 .361 N.N.W. 7.7 10 .347 N.N.W. 8.

11 29.324 N.W. 8.

12M. .295 N.W. 8.

1 .268 N.W. 1/2 W. 7.7 2 .252 N.W. by W. 7.5 3 .238 N.W. by W. 7.7 4 .223 N.W. by W. 1/2 W. 7.7 5 .220 W. by N. 1/2 N. 8.

6 .221 W. by N. 1/2 N. 8.

7 .225 W. by N. 1/2 N. 8.

8 .229 W. by N. 8.5 9 .233 W. 8.5 10 .243 W. 8.5 11 .256 W. 8.5 12 .282 W. by S. 9.

20th August to noon.

1 29.351 W. by S. 1/2 S. 9.

2 .363 W. by S. 9.

3 .375 W. by S. 9.

4 .413 W. by S. 9.

5 .437 W.S.W. 7.5 6 .457 S.W. by W. 7.

7 .457 S.W. 1/2 W. 6.

8 .471 S.W. 6.

9 .489 S.W. 1/2 S. 6.5 10 .505 S.W. 1/2 S. 6.5 11 .512 S.W. 1/2 S. 6.5 12M. .515 S.W. 1/2 S. 6.5

The barometric readings are corrected to the freezing-point density of the atmosphere, as also to the level of the ocean, and are further reduced by comparison with the Standard Barometer at the New Observatory. They are also relieved of a source of error arising from the regular decline for each day of the barometer, as evidenced by the observations made during June and July, 1858, in mean lat.i.tude 23 52' N., mean longitude 119 12'

E. This downward tendency will be apparent from the following readings for each hour:--for 1h. (A.M.) - 0.004, 2h. - 0.005, 3h. - 0.0012, 4h. -0.015, 5h. - 0.012, 6h. - 0.006, 7h. - 0.02, 8h. - 0.012, 9h. - 0.021, 10h.

-0.02, 11h. - 0.018, noon - 0.015, 1h. - 0.008, 2h. - 0.007, 3h. -0.021, 4h. - 0.025, 5h. - 0.023, 6h. - 0.015, 7h. - 0.008, 8h. - 0.001, 9h.

-0.008, 10h. - 0.014, 11h. - 0.015, 12h. (midnight) - 0.011. These quant.i.ties are to be read as implying that when added to or deducted from those supplied by actual observations, they result in the quant.i.ties already a.s.signed as the corrected averages for the day. The direction as well as strength of the wind are copied from the averages as calculated by the Commodore from the s.h.i.+p's log, the meteorological journals and the daily postings made by the Commodore himself.

According to the delineation of the path of the cyclone, as prepared from the observations recorded, the following table, already referred to, gives the approximative distance of the s.h.i.+p at stated points from such central path, as compared with that deduced from barometrical observations, allowing for the differences already mentioned. In the case of the wind-pressure, the average is deduced from the mean of successive observations taken every hour, and for the most part divided into intervals of three hours each.

Distance. Air- Difference. Distance pressure. according to curve.

1 17th August 4 A.M. 336 29.915 in. 336 2 " " noon. 297 .860 0.055 300 3 18th " midnight. 265 .783 .132 257 4 " " 6 A.M. 230 .736 .178 233 5 " " 9 A.M. 205 .667 .248 205 6 " " 6 P.M. 153 .438 .477 153 7 19th " 3 A.M. 140 .335 .580 138 8 " " 5 A.M. 148 .364 .551 142 9 " " 8 A.M. 146 .373 .542 143 10 " " noon. 125 .296 .619 130 11 " " 3 P.M. 123 .238 .677 122 12 " " 6 P.M. 134 .222 .693 138 13 " " 9 P.M. 148 .235 .680 144 14 20th " midnight. 183 .296 .619 183 15 " " 6 A.M. 313 .450 .465 313

The minimum pressure according to the curve would be 28.975, but must actually have been less. According to the strict reading it would result that all radii before reaching the point where nearest the central path, as also all those in the same half-circle after such central line has been crossed, should have the same value, whatever the direction, which if rigidly a.s.serted cannot be correct, since the motion of a cyclone is truly circular only in the immediate vicinity of its central point. As that point is receded from, the motion becomes more or less elliptical, as is attested by the barometric differences, which had the cyclone been a true circle in all its parts ought to be similar for similar distances. This it is admitted is not the case, as the barometric pressure shows a marked decline in the earlier part of a cyclone the more rapidly the central line is approached, just as it rises again once that line has been pa.s.sed.

For this reason the distances as a.s.signed upon a line of curves deduced from the foregoing observations must be too great, especially those which are calculated at right angles to the path of the typhoon, because perpendiculars drawn at right angles to the varying directions of the wind must intersect each other at points more distant than the actual central point of the cyclone itself.

To the foregoing may be appended a few extracts recounting the damage done by the great typhoon of 27th July, 1862, from which some idea may be formed of the tremendous violence and destructive effects of this description of atmospheric agency.

_From London and China Telegraph, 29th Sept., 1862._