23

present ease, shows that the position of this arrow is between northwest and north-northwest—about 4° west of the latter point. By making the plain end of the second needle pass throughthe interpolated point the observer would have found that he had then the vortex to the south-southeast. For the use of Fournier’s rule the two observations furnished the following data:

September 6, 8 p.m.: Barometer, 29.42 inches; wind, NE.September 7, 7 a.m.: Barometer, 28.22 inches; 'wind, N. by E.

The ship being between 25°—32° (at least on the 7th), and September belonging to GroupIII, the value of P was 29.65 inches.

Hence,

29.65—28.22 100 _

29.65 —29.42 x ''' X ~~ '

[ 2 /= 20 ]

With disposition of the apparatus as described, the small needle pointing to 19 on the gradu-ation of the graduated needle would have shown the track of the cyclone to be south by west to northby east. However, the course of the ship during the interval between the two observations, whichwas south by east, would have had to be taken into consideration. On account of this course theinstrument would have shown a less inclination of the track to the northeast than it actually had.The composed direction was north-northeast. (See PI. XL.)

The vortex was, therefore, recurving to the west of the ship, as was shown in the WeatherBulletin for September, 1902, issued by the Philippine Weather Bureau.

(5) (a) At noon July 26, 1902, the barometer on board the steamship Loonsang was 29.33inches, and the wind blew from west by north; she was in zone C. At 3 p. m. the barometer hadfallen to 29.22 inches, and the wind had backed to southwest. By Fournier’s rule w r e have:

29.73 — 29.22 100

- = _ • r — 7R

29.73 — 29.33 x ' ' ‘

The position of the needles would have been as shown on Plate XLIII, the resulting directionbeing east by south—west by north.

The calculation with readings corrected for daily oscillation gives a somewhat different result.Since the ship was below the twenty-first degree of north latitude, we take the corrections from theManila table:

July 26, noon, 29.33—0.02 inches = 29.31 inches.

July 26, 3 p.m., 29.22 -(-0.02 inches =29.24 inches.

Hence,

29.73 — 29.24 100

29.73 — 29.31 y

The direction corresponding to this value of D 2 is shown on the plate by means of a dotted line.

(6) On the same day, July 26, at 3 p. m. the barometer of the steamship Rosetta Mara stood at29.22 inches, and the wind came from north-northwest. At 6 p. m. the barometer indicated 29.12inches, with the wind blowing from northeast.

Fournier’s formula gives,

29.73 — 29.12 100

29.73 —29.22~ x

[y— so]

The track resulted, therefore, as shown by the small needle on Plate XLIV, east-northeast bynorth to west-southwest by south. But owing to the ship’s course being almost opposite to themotion of the vortex (see PI. XL), the composition of the two motions will give the true directionof the track, which in the present case will be east by south to west by north, as was the casewith the Loonsang.