24
(c) On the 27th at 3 a. m. the barometer reading on the Rosetta Mara was 28.85 inches withwind coming from southeast. Comparing this observation with the one made at 6 p. m. on thepreceding day, we find by Fournier’s rule:
29.73 — 28.85 100
29.73—29.12 x '
b =70]
The small needle will point to northwest, and, composing this with the ship’s course, we findthat the average direction of the center from 6 p. m. of the 26th till 3 a. m. of 27th was northwestby west. (See PI. XLIV.)
(6) Another typhoon which was felt so severely in Hongkong in the beginning of August,1902, crossed to the north of Aparri on the evening of July 31. The trajectory found by meansof the barocyclonometer was east by south to Avest by north. Aparri Avas successively in zones Aand B from July 31 to August 1, and the following observations Avere made:
July 31, 10 p.m.: Barometer, 751.1 millimeters; Avind, NW. 1 / one BAugust 1, 6 a. m.: Barometer, 746.4 millimeters; Avind, WSW. J
Whence Ave have,
755—746.4 100 .
755—751.1 x ’ '
Applying the corrections for daily oscillation Ave obtain the folloAving:
July 31, 10 p.m.: 751.1—0.9 =750.2 millimetersAugust 1, 6 a. m.: 746.4 — 0.0 =746.4 millimeters
Avhich gives y= 55.
The tAvo resulting directions are shown on Plate XLY.
(7) Observations made on board the German cruiser Hertha furnish some very interestinginstances concerning the use of the barocyclonometer. From observations made at Nagasaki (seeNo. 8) Ave learn that that harbor Avas within zone A of a typhoon (passing afterwards close by tothe south) on the morning of August 8, 1902. Hence the Hertha , which had left Nagasaki at 3.25p. m. of the 7th, and was some hundred miles to the southeast by south of the port at noon ofthe 8th, found herself far within zone A. In fact at 8 p. m. of the 8th the barometer showed 751.79millimeters—that is, between zones A and B—and at midnight it had fallen to 748.87 millimeters.By that time the ship had entered zone B. By taking the readings and wind*directions we can findthe bearing of the center of the typhoon at the corresponding hours.
OBSERVATIONS MADE ON BOARD THE GERMAN CRUISER HERTHA.
No.
Date.
Barom-
eter.
Wind.
Zone.
Fournier’s
formula.
Trackof centerto—
Approx-imatedistanceof center.
Day.
Hour.
Uncor-
rected
read-
ings.
Cor-
rected
read-
ings.
Mm.
Miles.
i
Aug. 8
Midnight.
748. 87
ESE.
B.
138
2
Aug. 9
2. 00 a.m.
745. 61
ESE.
C.
118
3
_clo_
5. 30 a.m.
743. 01
SE. by E.
c.
74
73
NE.
79
4
_do_
7. 30 a.m.
740. 58
E.
c.
80
78
NE. by E.
55
5
_do_
8. 30 a.m.
739. 85
ESE.
c.
94
93
NE. by E.
42
6
_do_
10. 00 a.m.
730.99
SE. by E.
D.
60
60
NE. by E.
21
7
_do_
11. 45 am.
712. 37
SE.
D.
54
55
NE. bv E.
8
Observations 1 and 2 can not be combined for a determination of the direction of the trajectorysince the wind had not changed during the interval.
The combination of readings 2 and 3 furnishes a remarkable instance of the influence of theship’s course upon the trajectory as found by means of the instrument. The small needle pointingto 74 gives the direction south by west and north by east, the course of the ship being almost south-