E. Loomis— Barometric Gradient in great storms. 449 
the ocean. In 1880, Feb. 29th, in lat. 612° N. and long. 25° E. 
the barometer fell to 719™, and in 1881, March 19th, in lat. 
64° N. and long. 394° E. it fell to 709™™. The last storm was 
remarkable for an increase of intensity in its progress eastward 
over the continent. When it left the Atlantic Ocean the pres- 
sure at the center of the storm was 728™™, and the pressure fell 
to 709™™ (27-9 inches) as the storm advanced eastward. Over 
the United States the barometer never falls so low. In m 
eighth paper I gave a list of all the cases in which, at any of 
the Signal Service stations, the barometer fell as low as 29-25 
inches during a period of two years. This list shows only 
twenty-eight cases in which the barometer fell below 29:00 
Inches; it shows sixteen cases in which: the barometer fell 
below 28-9. inches; it shows five cases in which the barometer 
fell below 28-8 inches, and only three cases in which it fell be- 
low 28-7 inches. These three cases occurred Nov. 18, 1878, at 
the first, second and third observations for that day, the lowest 
pressure being 28°47 inches at Eastport, Me. According to the 
record of Mr. R. T. Paine, the lowest point which the barom- 
eter at Boston has reached during the-past sixty years, is 28°47 
inches (Nov. 25, 1846), and this is probably as low as the 
barometer has fallen in that part of New England at any time 
since reliable barometric observations have been made. There 
1s no doubt that the geographical extent of areas of low pres- 
sure is considerably less in the United States than it is in 
Northern Europe, and I think the cause is to be found in the 
permanent ridge of high pressure prevailing in the southern 
portion of the United States. My twelfth paper was accom- 
panied by a chart showing that during the colder months of 
the year there is a ridge of high pressure which is extremely 
persistent between the parallels of 30° and 35°. When the 
center of a great storm is near lat. 45°, the area of low pressure 
seldom extends much below the parallel of 35°. It may be 
inferred that if a storm center should pass farther north, the 
storm would attain greater dimensions and there would bea 
greater depression of the barometer at the center. This conclu- 
sion is certainly correct for the eastern border of the American 
Continent, particularly for the neighborhood of Greenland ; and 
1t 1s probably true (though in a less degree) for the interior of — 
the continent; but on account of the lack of observations we 
cannot make a very satisfactory comparison. 
The column marked @’ in table I was computed from Fer- 
rel’s formula, assuming that for pressures above 760™, the 
Second term of the formula should be taken with a negative 
Sign. A careful examination of this table will show that for 
pressures above 760™ the second term should be omit 
entirely. It is evident that if the circulation of the air about 
Am, Jour. sag a ear SERIES, Vou. XXVI, No. 156.—Dxc., 1883. 
