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The winter oscillations up to lat. 65° are pretty well represented by the formula:

W = 1.890 sin 27 +0.104 cos2l,

and the summer oscillations by the formula:

S 1.000 sinal +0.104 cos' l.

=

The differences between the observed and computed values are shown in columns fifth and seventh in the above table. These results indicate a steady increase in the mean monthly oscillation up to about lat. 65°, and from that point the oscillation diminishes as we proceed northward. The term 0·104 cos27 represents approximately the diurnal oscillation of the barometer, and the

60°

Storms on the Atlantic Ocean by Maury's Charts.

80° 75° 70° 65° 60° 55° 50° 45° 40° 35° 30° 25° 20° 15° 10° 5°W. 0°

60 102 123| 117 781 30

16 38 35 31

27 37 28 27

55

150 420 510 694 850 932 1260 1393 583 57 111 140 169 159 117 152 133 46 38 26 27 24 19 12 12

50

126 288 919, 1242 1570 1740 1627 1539 1475 1312 920 313

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other term of the formulas varies as the square of the sine of the latitude, and this law of increase holds pretty closely up to about latitude 65°. That part of the barometric oscillation represented by the first term of the formula is the effect of storms, and the oscillation diminishes within the Arctic circle. These results seem to indicate that in the Northern Hemisphere, storms increase in frequency as we proceed northward as far as latitude 60° and perhaps somewhat farther. The same result is shown by Maury's storm chart of the North Atlantic. The preceding table presents a summary of the results of this chart. The ocean is divided into squares by parallels of lati tude drawn at intervals of five degrees from each other, and meridians of longitude at intervals of five degrees. Each square of the preceding table contains three numbers. The first shows the number of observations within the given square, each observation representing a period of eight hours. The second shows the number of gales reported, and the third is the average number of gales occurring in a hundred observations. Thus in the square included between the parallels of 40° and 45° of north latitude, and between the meridians of 45° and 50° west longitude from Greenwich, the first number is 1863, which shows the number of observations obtained in that square. The second number is 280, which denotes the number of gales reported; the third number is 15, which denotes that the number of gales was 15 per cent of the whole number of observations. An inspection of this table will show that on each meridian the frequency of gales increases with the latitude up to the highest latitude from which observations are reported.

Storms traced across the Atlantic Ocean.

When storms from the American continent enter upon the Atlantic Ocean they generally undergo important changes in a few days and are frequently merged in other storms which appear to originate over the ocean, so that we can seldom identify a storm in its course entirely across the Atlantic. The following are the only cases I have found on the French and Danish charts (embracing a period of 27 months) in which storms can be pretty distinctly traced across the Atlantic.

1. Nov. 30-Dec. 11, 1864. A storm traced from Newfoundland to Ireland.

2. April 20-May 3, 1865, traced from Labrador to Ireland.
3. May 26-29, 1865, from Gulf St. Lawrence to Ireland.
4. Oct. 2-10, 1865, from Cape Cod to Ireland.

5. Oct. 11-17, 1865, from Newfoundland to Ireland.
6. March 1-5, 1874, from Hudson Bay to North Cape.
7. April 14-17, 1874, from Hudson Bay to Norway.

8. April 16-23, 1874, from Gulf St. Lawrence to Norway. 9. May 23-30, 1874, from Gulf St. Lawrence to Norway. 10. Aug. 1-4, 1874, from Gulf of St. Lawrence to North Cape.

11. Aug. 12-17, 1874, from Hudson Bay to Norway.

If the observations each day were sufficiently numerous to show the isobaric curves for every part of the Atlantic Ocean, doubtless many more storms might be traced from America to Europe, but it is presumed that such cases do not occur on an average more than once or twice a month. The storms of Europe generally have their origin considerably east of the American Continent and soon become so violent as to draw within their influence any small barometric depression which started from America.

Velocity of Ocean Storms.

The average velocity of storms upon the Atlantic Ocean as deduced from 134 cases on the French maps is 19.3 miles per hour; the velocity deduced from 49 cases on the Danish maps is 20.3 miles per hour; giving an average of 19.6 miles per hour from both series of maps. The average velocity for the storms of the United States as deduced from 485 cases is 26 miles per hour. hour. From a considerable number of cases in Europe, Prof. Molin has deduced an average velocity of 267 miles per hour. These numbers indicate that storms travel with less velocity over the Atlantic Ocean than they do over the Continents of America and Europe; and it seems to follow that the progressive movement of a storm is not the result of a simple drifting of the atmosphere; for it seems probable that the aver age progress of the atmosphere in an easterly direction is as rapid over the Atlantic Ocean as it is over North America.

Storms of Jan. 29-Feb. 8, 1870, on the Atlantic Ocean.

A succession of storms of unusual severity passed over the Atlantic, between Jan. 29 and Feb. 8, 1870, an account of which has been published by Capt. Henry Toynbee, of the London Meteorological office. On the 30th of January an area of low barometer prevailed near Nova Scotia; on the 31st it was east of Newfoundland; and on the 1st of February it was merged in another storm which had prevailed for several days on its eastern side. On the 2d of February a second storm center appeared near Newfoundland; on the 3rd it had advanced east about 700 miles; and on the 4th it became merged in another storm off the Irish coast.

On the morning of the 5th a third storm appeared near the center of the Atlantic, which must have developed with unusual rapidity, since on the preceding day, observations had indicated no great atmospheric disturbance in that neighborhood.

The isobar of 29 inches is shown on the accompanying chart. On the afternoon of the same day, this storm blended with another storm on its eastern side, and there resulted one of the most violent hurricanes ever experienced on the Atlantic Ocean. At 6 P. M. the barometer fell to 27-33 inches, which Capt. Toynbee pronounces the lowest ever observed on this part of the Atlantic. The accompanying chart represents the isobar of 29 inches on the morning of the 6th, when the diameter of this curve was over 1000 miles, and the diameter of the isobar of 30 inches was over 2000 miles. During the next two days the storm advanced slowly towards the southeast, and its severity was much diminished. The accompanying chart shows the isobar 29.5 inches on the morning of Feb. 8th. During this interval of three days the center of the storm had moved only about 900 miles, showing an average velocity of about 12 miles per hour.

Application of Ferrel's formula.

In vol. viii of this Journal, p. 343, Prof. Ferrel has given a formula which enables us to compute the depression of the barometer resulting from a violent storm. If we divide the denominator of this formula by the number of inehes in a mile, and suppose the wind to move in a circle, the formula becomes

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where G is expressed in inches, but v and r are expressed in miles. I have applied this formula to the storm of Feb. 5th, 1870, and the results are shown in the following table. Column first shows the isobars which have been selected as the basis of comparison; column second shows the radius of each isobar as nearly as can be determined from the observations of Capt. Toynbee's memoir; and column third shows the velocity of the wind in miles on each of these isobars. These velocities were obtained by taking the mean of the various observations corresponding to the barometric heights given in column first. These velocities were recorded in the numbers of Beaufort's scale (0-12) and were reduced to miles by the table in Scott's Met. Instruments, p. 58. Column fourth shows the gradient to 100 miles computed by the above formula, for points midway between the several isobars selected. If this gradient be supposed to be maintained for a distance equal to the distance between the isobars, it will show a change of barometric pressure about the same as that actually observed. For the inner circle, the computed gradient will represent the observed depression of the barometer if we suppose that near the center of the storm there was a considerable mass of air revolving with a diminished velocity.

Radius of
Isobar.

Miles.

Ex. 1.-Storm of Feb. 5, 1870, Atlantic Ocean, lat. 51° 3' N.

Barometer.
Inches.

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formula to two viocoast of the United In the Punta Rassa

I have made a similar application of the lent cyclones of recent occurrence on the States, and the results are shown below. cyclone the assumed velocities 90 and 70 miles agree pretty well with the velocities actually observed; the velocities 50 and 35 miles are somewhat greater than the observations at the surface of the earth, but may be presumed to have been the velocities at a little elevation above the earth's surface. The velocities assumed for the Indianola cyclone are the velocities actually observed or estimated at Indianola.

Ex. 2.-Storm of Oct. 6, 1873, Punta Rassa, lat. 27° 0'.

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Ex. 3.-Storm of Sept. 16, 1875, Indianola, lat. 28° 31'.

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The following is an example of a great inland storm of unu sual severity. Column third shows the greatest velocity of the wind observed at any station near the corresponding isobars in column first, and column fourth shows the velocity assumed in computing the gradients in column fifth.

Ex. 4.-Storm of Nov. 18, 1873, New England, lat. 41°

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