The experiment of Wednesday was rendered abortive by the accidental occurrence of a thunder-storm which could not be foreseen. At this season of the year thunder-storms occur generally in the after part of the day or night, and I would therefore advise that the balloon be filled immediately after the clearing off of the sky, and then used as soon as possible after daylight the next day.

Mr. Lowe came to this city with the implied understanding that, if the experiments he exhibited to me were successful, he would be employed. He has labored under great disadvantages, and has been obliged to do all that he has done, after the first experiment, without money. From the first he has said that the balloon he now has was not sufficiently strong to bear the pressure of a hard wind, although it might be used with success in favorable situations and in perfectly calm weather. I hope that you will not yet give up the experiments, and that you will be enabled with even this balloon to do enough to prove the importance of this method of observation, and to warrant the construction of a balloon better adapted to the purpose.

I remain, very truly, your obedient servant,

JOSEPH HENRY.

Up to this time I had used my own machinery, and had a party of persons constantly employed at my own expense to assist in the management of the balloon and to keep it in order.

On the 2nd of August I called on Major Hartman Bache and gave him a detailed account of what I had accomplished, also getting forth the advantages of using balloons, provided proper facilities were afforded. Upon this Major Bache gave me a letter to Captain Whipple, authorizing him to direct me to construct such a balloon as I desired; upon the receipt of which the latter gave me the following order and instructions:

HEADQUARTERS DEPARTMENT OF NORTHEASTERN VIRGINIA,
Arlington, August 2, 1861.

Mr. T. S. C. LOWE,

Aeronaut:

SIR: You are hereby employed to construct a balloon for military purposes capable of containing at least 25,000 cubic feet of gas, to be made of the best India silk, not interior to the sample which is divided between us, you retaining a part, with besof manila cordage from 1,200 to 1,500 feet in length. The materials you will purchase immediately, the best the markets afford and at prices not exceeding ordinary rates; and the bills you will forward to me through Major Hartman Bache, chief of the Corps of Topographical Engineers. When these materials shall have been collected at Philadelphia, where the balloon is to be constructed, you will report to me, that I may send an officer of the corps to inspect them. You need not, however, wait for the inspecting officer, but go on rapidly with the work, with the understanding that it may be suspended, provided that upon examination the materials or work prove unsatisfactory.

Your compensation from the day of collecting the materials and during the time of making the balloon shall be $5 per day, provided that a reasonable time be allowed for the collection and ten days for making. From and after the day that the balloon shall be ready for inflation at Washington, D. C., your compensation will be $10 per day as long as the Government may require your services.

Inclosed herewith is an order authorizing the purchase of materials necessary for the operation with which you are charged.

Very respectfully,

A. W. WHIPPLE,

Captain, Topographical Engineers.

[Inclosure.]

HEADQUARTERS DEPARTMENT OF NORTHEASTERN VIRGINIA.

Mr. T. S. C. Lowe, aeronaut, is hereby authorized to purchase 1,200 yards of best India silk and sufficient linen thread, cordage, &c., for the construction of a balloon, and all reasonable bills for the same, when presented to me through the Bureau of Topographical Engineers, will be paid.

A. W. WHIPPLE,
Captain, Topographical Engineers.