66 U. S. COAST AND GEODETIC SURVEY 
by air line and considerably farther as measured along the coast line. Moreover, 
Baltimore lies on an arm of Chesapeake Bay 140 miles from the open sea, while Boston 
is less than 10 miles from the open sea. 
From Figure 30 it is seen that for the 27 years of observations at Boston, sea level 
for the year 1925 was lowest, while for the year 1945 it was highest, the heights on the 
tide staff being, respectively 8.03 and 8.53 feet. At Baltimore mean sea level for the 
epoch 1924-1942 reads 4.25 on the staff, while for the years 1925 and 1945 the yearly 
sea levels read respectively, 4.08 and 4.57 foot. The corrections for the two years are 
therefore +0.17 and —0.32 foot, respectively. This makes mean sea level at Boston 
from the 1925 observations 8.03+0.17=8.20 and from the 1945 observations 
8.53—0.32=8.21 feet. 
From the continuous series of observations at Boston the direct 19 year mean value 
of sea level for the epoch 1924-1942 is 8.21 feet on the staff. The yearly sea levels for 
1925 and 1945 which differed from each other by 0.5 foot thus give mean sea level values 
when corrected by comparison with simultaneous observations at Baltimore, which 
differ by 0.01 foot in the one case and agree exactly in the other case with the primary 
determination. 
If we take each of the 27 yearly values of sea level at Boston from1922 through 
1948 and determine mean sea level values by comparison with Baltimore, we find that 
on the average these values differ from the direct primary determination by 0.04 foot, — 
the largest individual difference being 0.13 foot. 
Had a station closer to Boston than Baltimore been taken, one more nearly subject 
to similar wind and weather conditions, closer approximation of the mean sea level 
values derived from a year of observations could be expected. Had New York been 
used, the mean sea level values from each year of the Boston observations would show 
an average difference from the primary determination of 0.03 foot, with the largest indi- 
vidual difference of 0.07 foot. 
We may test the applicability of the method of correction by comparison to 
stations on the Pacific Coast. As an example we may take San Francisco and Los 
Angeles which are about 350 miles apart. From Figure 32 it is seen that at Los Angeles 
sea level was lowest in 1933 and highest in 1941, the heights on the tide staff being, 
respectively, 6.27 and 6.73 feet. Taking San Francisco as the primary station, mean 
sea level for epoch 1924-1942 reads 8.67, while for the years 1933 and 1941, the yearly 
sea levels were respectively, 8.52 and 9.07 feet. 
The corrections to mean sea level for these years are thereforé +0.15 and —0.40 
foot. Applying these to the corresponding yearly sea levels at Los Angeles we derive 
mean sea level from the 1933 observations as 6.42 and from the 1941 observations as 
6.33. From the observations at Los Angeles from 1924 through 1942 the direct primary 
determination is 6.48. So that the two yearly values which differed from the mean value 
by 0.21 and 0.25 footrespectively, after correction differ from the mean value, respectively, 
by 0.06 and 0.15 foot. 
If each of the 25 years of observations at Los Angeles is corrected to a mean value 
by comparison with San Francisco, the average difference from the 1924-1942 mean is 
found to be 0.06 foot, the greatest difference being 0.15 foot for 1941. 
Had San Diego, which is only 100 miles away from Los Angeles, been used as the 
primary station, closer approximations would have been derived. At San Diego 
