ATMOSPHERIC PRESSURE 11 
Table 14. Phases of 12-hour waves of atmospheric pressure over South Pacific Ocean, 
Te 1928-29 
aha 
Latitude 
Phase angle 
0.6N 9.8 110.3 W 96.6 29 162.6 153.6 + 9.0 
11.78 8.3 126.7 W 95.2 45 153.7 155.1 - 1.4 
17.958 9.5 130.2 W 84.7 33 160.6 155.2 + 5.4 
30.6 S 9.5 100.2 W 33.1 22 150.0 153.6 - 3.6 
38.5 S 5.1 99.3 W 12.4 9 138.2 154.5 - 16.3 

2 Observed maximum amplitude occurs earlier than computed for positive difference, and 
later for negative difference. 
Table 15. Comparison of mean yearly phase angles of 12-hour wave of 
atmospheric pressure for Easter Island, Samoa, and Jaluit with those 
computed from Simpson’ s formula 

Easter Island 2758 109 W 
Samoa 14S 172 W 
Jaluit 6N 170 E 
(60° N, 1° W) are compared with those calculated for 
these locations, however, the observed phase angles 
(149°4 and 138°5, respectively) are smaller than those 
calculated. 
Summarizing the discussion of the 12-hour wave of 
atmospheric pressure, the following general conclusions 
may be presented: 
1. The amplitude of the 12-hour wave is less over the 
ocean than over land areas; the magnitude of the differ- 
ence is of the order of 0.1 mm. 
2. A comparison of the differences in amplitude at 
oceanic islands and for mean positions over the ocean 
indicates that the amplitude at island stations is of the 
order of 0.06 mm greater than at purely oceanic sta- 
tions. 
3. There appears to be a greater difference between 
the time of maximum amplitude of this wave between 
high and low latitudes over the ocean than is indicated by 
values computed after Simpson’s formula. 
The 8-hour Period 
As shown in figure 9, the phase angles and ampli- 
tudes of the 8-hour wave also show remarkable regular- 
ity. The phaseangleof this oscillation, for a given peri- 
od of the year, is opposite in the Northern and Southern 
hemispheres, and changes phase for any given hour be- 
tween winter and summer [15, p. 175]. The amplitude is 
greatest at latitude 30°. In summer the first minimum 
occurs at about 02h; in winter the first maximum occurs 
at this hour. Other maxima and minima follow at 8-hour 
intervals. The amplitude is smallest during the fall and 
spring months, and is always small at the equator. 
It is rather difficult to analyze the Carnegie pres- 
sure data for this third harmonic, inasmuch as the 
cruise was so planned that the vessel was in each Hem- 
isphere during the summer months, in order to avoid 
the stormier winter season. The Fourier coefficients of 
the 8-hour wave, however, have been determined and 

158.8 153.9 4.9 
160.0 156.4 3.6 
165.6 155.4 10.2 
plotted in figure 9. The figure includes notations of the 
months during which the observations were made within 
each range of latitude. During the southern summer at 
latitude 30° south, the amplitude would be expected to 
be at a maximum; this is confirmed by the large ampli- 
tude (0.114 mm) shown on the harmonic dial for the mean 
position 30° south, during the months of November, De- 
cember, and January. At the mean position latitude 30° 
north, observations were made during the months from 
May to October; the mean amplitude, therefore, is small 
(0.007 mm) since it is a resultant of waves of opposite 
seasons. 
The preponderance of observations made during the 
summer season is apparent in figure 9. The crests of 
the first wave at all mean positions in the Southern Hem- 
isphere and also at latitudes 20°, 40°, and 50° north oc- 
cur between 05h 33m and 07h 17m (first minimum, 
therefore, around 02h), as would be expected during the 
summer season in either Hemisphere. 
These results are in agreement with the conclusions 
drawn by Hann [16] and Sverdrup [17] from their careful 
analyses of the 8-hour pressure oscillation. 
The 6-hour Period 
The 6-hour pressure oscillation has been discussed 
thoroughly by S. K. Pramanik [18], who has compiled 
data from 136 stations well distributed with respect to 
season, latitude, and proximity to sea and land bodies. 
He concludes: 
1. The mean annual amplitude, a4, does not vary a 
great deal with latitude between +50°, though it appears 
to have a maximum at about latitude 25°. 
2. There is considerable seasonal variation in a 4> 
the winter greatly exceeding the summer values,- more 
particularly at inland stations. The mean winter and 
summer values between +59° latitude are respectively 
0.051 mb and 0.011 mb at coast stations, and 0.059 mb 
and 0.009 mb at inland stations. The winter amplitude 
