Its velocity in a direction from south to north was twenty-four miles per hour. Calculations made from various data show that the velocity of the wind in its rotary motion was from one hundred to one hundred and fifty miles per hour.

THE TORNADO OF APRIL 17, 1882, COMMONLY KNOWN AS THE GRINNELL TORNADO."

On June 17, 1882, a terrible tornado swept over the western portion of Boone county, through Story county, and thence in a southeasterly direction to Mt. Pleasant in this State. It was first seen in this county about four miles south of the College, and had the appearance of a long, slender column reaching from the clouds to the earth. The column was nearly a mile long, and perhaps four hundred feet in diameter. In passing through this township it broke into two distinct tonadoes, which moved nearly parallel about two miles apart, and then united after crossing the Skunk river. Probably ten thousand dollars would not pay the damage done in this county alone.

I shall only give a brief summary of the important peculiarities and facts of this tornado.

First-Its general direction was from northwest to southeast.

Second-The wind rotated from right to left, or, in the opposite direction of the hands of a watch.

Third-The cloud moved over the State at the rate of about fortysix miles per hour.

Fourth--The velocity of the wind in the tornado was from two hundred to three hundred and fifty miles per hour.

Fifth-At times the tornado resembled a funnel with the little end down; then a long serpent, and then at other times it resembled two cones with their bases on the ground and in the clouds meeting in mid-air.

Sixth-The width of the tornado varied at different times from two hundred to one thousand feet.

Seventh-It frequently rose from the ground and drew into the clouds, and after passing some distance the funnel would let down again and commence its work of destruction.

Eighth-This tornado swept through the town of Grinnell in Poweshiek county, and killed and injured a large number of people. It is probable that not less than half a million dollars worth of damage was done in its course through Iowa.

TABLE NO. I.

Table showing the mean annual temperatures, and also the mean monthly temperatures, from 1876-1883. Annual mean temperature for seven years, 48.12°.

*The observations for 1883 not completed at the time of publication.

TABLE No. II.

Table showing the mean temperature of the seasons from 1876

1873.

In getting the mean temperatures of each winter the mean temperature of December of the previous year is included.

Winter..
Spring..

1876. 1877. 1878. 1879. 1880. 1881. 1882. 1883. Means

Summer.

Autumn.

24.3 18.6 31.1 17. 26.2 14.61 28.6 11.7 21.5
46.1
45.2 51.4 49.9 49.6 45.9 46.4 45.2 47.
73.6 71.3 73.5 73.6 74.7
71.3 73.2
45.4 48. 49.2 51.1 44.

76.
50.5

71.5

51.5

*

48.5

*Not completed at time of publication.

YEARS.

471

-1259--1048

-10 61

25 87

3192

41 76

28 62

-164 9

92

-19

56-659

770 23 78

16 45-15

-30 44-1476-183

368-464

-541-18

43-955 -659

-211391

301731 36

The sign minus (-) means below zero,

TABLE No. IV.

Table showing the dates when the earliest and latest frosts occurred for seven years.

YEAR. April. May. June. July. August.

Table showing the monthly and mean annual rainfall for the years 1876-1883. The mean annual precipitation in inches for seven years is 35.22 inches. Snow is melted and measured as water.

*Observations for 1883 not complete when published.

The heaviest rainfall in eight years was in 1881, when it amounted

to 51.94 inches. The least was in 1880, 29.5 inches.

The largest amount in one month was in July, 1881, 16.31 inches.

5.75

1.20

2.07 2.17

0.98

TABLE No. VI.

Table showing the amount of rainfall, in inches, for the seasons from 1876-1882.

Winter..

Spring.
Summer

Autumn

1876. 1877. 1878. 1879. 1880. 1881. 1882. MEANS.

4.

0.42 2.10 2.34 2.52 3.02 2.60| 8.07 7.80 11.83 6.51 6.07 5.67 10.74 19.07 18.02 14.86 9.11 12.57 26.26 12.24 7.61 4.73 4.7311.74 8.72 15.94 6.42

The greatest rainfall occurs in summer, and the least in winter. In spring the amount is about the same as in autumn.

2.42

8.08

16.02 8.55

TABLE NO. VII.

Table showing the mean daily humidity for the months of April to October, from 1877-1883.

These observations are not taken during freezing weather.

Observations taken at Tabor, Fremont county, Iowa, by Dr. J. F. Sanborn, for four and one half years. Latitude, 40°, 50'; longitude, 95°, 40'. Height above the sea, 1,200 feet.

The first column of figures gives the mean height of the barome ter for the month, corrected for temperature only. Then follows the mean temperature for the mouth; the mean wind velocity for the month; the per cent of cloudiness, on a scale of 10; the total rainfall for each month; the number of rainy days, and of days when snow fell.