Box 7, Folder 5: Correspondence 1840-1843

Milwaukee Wisconsin Mar. 31 1840 Dear Sir

I have received your interesting pamphlet on the plants of Franklin County and it would afford me pleasure to exchange with you any plants found here for those of your neighborhood which I have not already in my herbariums. To [enable?] you to ascertain whether we have anything that will be interesting I send a Catalogue of our plants, which please return with some mark opposite the species you want. I send also your pamphlet with a mark (o) opposite those for which I would be willing to send Milwaukee plants in exchange. This I wish you would also return to me.

Please remember me to your father's and all other friends.

Very truly yours

I.A. Lapham

Wm. [G?] Sullivant Esqr.

To Wm. S. Sullivant. Mar. 31 1840

Cincinnati, May 28, 1840

Dear Brother

Your letter of the 13th instant is at home; and I am engaged in answering it by the employment of this first leisure moment. Perhaps I may not succeed in writing a very long or a very interesting letter, but I have a fancy that I can at least make it equal to yours in both these respects.

I have lately attended a course of lectures delivered by Mr. James P. Espy of Philadelphia on the Law of Storms, and I have been much instructed and interested in the theory which he labors to establish. He states no proposition but such as he can prove by facts and experiments; and all his propositions and deductions are based upon the laws of the exact sciences; "there's no speculation in it." I will attempt to write out from memory the fundamental propositions of his theory, hoping that you may take some interest in knowing some thing of the peculiar views of this gentleman, which are entirely novel and somewhat at variance with the commonly received opinions of the law of storms. 1st. Prop. That the atmosphere is capable of containing and does always contain a certain quantity of water in the form of invisible vapor. 2nd. That this capacity of the atmosphere for containing water increases rapidly with the temperature. 3rd. That the quantity of water actually in solution in the atmosphere varies greatly at different times and places, independently of the temperature, the air at a given temperature sometimes being filled nearly or quite to the extent of its capacity while at others it falls far short of it. 4th. That if from any cause, the temperatures of a portion of air containing a given quantity of vapor, be reduced to a certain point, that is, until the capacity be brought to the dew point, it must deposit a portion of its water. 5th. That expansion arising from diminished passage is attended by diminished temperature, that the actual diminution of temperature on this account in ascending from the surface of the earth is about one degree for every hundred yards; and that consequently air highly charged with vapor, that is with a high dew point, would not have to ascend very far before condensation would commence.

6th. That the condensation of vapor is attended with the disengagement of a very large quantity, more than a thousand degrees of latent heat, in other words, sufficient part is set at liberty by the condensation of a given quantity of vapor, to raise the temperature of a hundred times that quantity of water ten degrees. 7th. That when a portion of the air at the surface of the earth, becomes more rarified than the surrounding air, it ascends. These are the main propositions of Mr. Espy's theory, and they have been demonstrated a thousand times—indeed, they are almost self evident truths of themselves. When these propositions are admitted to the [truth?] we are then [illegible] to present the following modus operandi of the formation of clouds and rain. When the sun rises, the air at the surface of the earth becomes heated and from various causes may be unequally heated, and the portions more rarified than others ascends in columns as it were:—As the heated air rises up above the surface of the earth it comes under diminished pressure:—when it comes under less pressure it expands:—As it expands it becomes colder:—When it becomes as cold as the dew point, the vapor in the air is condensed into fine particles of water and forms visible cumulus clouds; and as this process continues, the clouds become surcharged with this condensed vapor, and the surplus descends to the earth in the form of rain:—Owing the formation of the clouds, the air gives out its latent [caloric?], and increased by that means the expansion of the air since the condensing of the vapor, and causes the upper portions of the forming cloud to swell out on every side and assume the shape of a large mushroom, which greatly increases the upward tendency of the air underneath the center of the cloud, and in consequence of the upward current of the air or water at the center, rising up and expanding out at the top, the air rushes inwards at the bottom from all sides to supply the vacuum,

Mr. Espy contends this is the true law of all storms, from the inefficient formation of the most simple cloud, to the most furious and devastating tornado. The facts experiments and arguments which he addresses in support of this theory are abundantly conclusive. He says that all the known phenomena of storms go to establish his theory, and his theory accounts for and explains all the phenomena

attending all storms the formation of rain and hail, the rising & falling of the barometer, life.

[diagram/figure]

The figure will serve to illustrate the modus operandi of the formation of clouds and rain. Let a portion of the air at the point a on the surface of the earth become more heated than the cold air will press in from all sides to supply its place. It is known that the air becomes colder at the rate of one degree for ever hundred yards in height up to the time of [perpetual?] congelation. If the temperature of the dew point is ten degrees below the temperature of the air at the surface of the earth, then when the ascending column of rain has reached the height of 10 hundred yards, the invisible vapor which it contains would begin to condense and form water & become visible. But as the air ascends the pressure is diminished and it expands & becomes colder and when it becomes colder it condenses the vapor & by this condensation a large quantity of lateral calorie is [evolved?], so that from the bottom to the top of the cloud the temperature diminishes in but half the ratio that it does below the being the cloud. The upper part of the cloud, therefore, will have a higher temperature than the surrounding air, and the [illegible] [lower?] and the expansion is increased from the cause & produces a violent upward current of air &c&c. Let an observer be situated at b with a barometer. If the storm approaches from the west, he will observe his barometer to fall and the wind to be blowing from the east. And when the storm has advanced to bring a to b, the barometer