128 REPORT—1843. 
Report of the Committee for conducting Experiments with Captive 
Balloons. 
TuE requisite apparatus is nearly complete. The balloon, 18 feet in diameter 
and 25 feet high, has been received at Woolwich by Colonel Sabine. Mr. 
Wheatstone’s electric thermometer has been tried, and found to act in the 
most perfect manner at distances of some miles, and we have ordered the 
addition of another part for giving the hygrometric indications. A series of 
experiments has been made on the strength and weight of cordage of various 
kinds of fibre; the proper quality has been decided on, and I am happy to 
state that Mr. Enderby, who has taken great interest in these inquiries, will 
present the necessary quantity of it to the Association. 
Of the original grant of 2501, 810. 8s. have been expended. 
The Directors of the Woolwich Gas-works have shown every wish to ac- 
commodate us, and assisted us in our preliminary experiments so as to make 
the inflation of the balloon perfectly manageable. 
To complete the advantages of our position at Woolwich, I would suggest 
it as extremely desirable that a request should be made by the Association to 
the Master-General of the Ordnance, entreating his assistance. 
T. R. Roginson, 
August 17, 1843. Chairman of the Committee. 
Appendix to the Report, by Professor WHEATSTONE. 
Tue Telegraph Thermometer which is intended to be carried up by the bal- 
loon, weighs, with its case, about four pounds. It is thus constructed :—The 
movement of a small clock causes a vertical rack to ascend and descend re- 
gularly in six minutes, three minutes being occupied in the ascent and three 
in the descent. The rack carries a fine platina wire, which moves within the 
tube of a thermometer; the extent of motion of this wire corresponds with 
28° of the thermometric scale, but it is capable of adjustment so that it may 
pass over any 28° of the range. ‘Two very fine copper wires, covered with 
silk, and of sufficient length to reach from the ground to the balloon when at 
its greatest elevation, are connected with the instrument in the following man- 
ner :—The extremity of one wire is connected with the mercury in the bulb 
of the thermometer, and that of the other wire with the frame of the clock, 
which is in metallic continuity with the platina wire. On the ground the 
lower extremities are united together; in the wire, whose opposite end is con- 
nected with the mercury in the thermometer, a sensible galvanometer is in- 
terposed, and in the course of the other wire a single, very small voltaic ele- 
ment is introduced. The galvanometer having been properly adjusted to its 
zero point, it will remain so during the time that the platina wire is not in 
contact with the mercury in the tube, but the needle will deviate as soon as 
the contact takes place, and will remain deflected until contact is again 
broken during the ascent of the rack. During each half-second of time, cor- 
responding with the beats of the clock, the wire moves through the 360th 
part of its range, and a different point of the range consequently corresponds 
with a different beat or half-second of each alternate three minutes. If, there- 
fore, an observer below be furnished with a chronometer timed to coincide 
with the clock in the balloon above, and note at what instant the needle of 
the galvanometer is deflected, he may infer from that observation the tempe- 
rature indicated by the thermometer in the balloon; for according to the dif- 
ferent expansion of the mercury in the thermometer the contact is broken at 
a different half-second. Should the rates of the two time-pieces not exactly 
correspond at the conclusion of a series of observations, the results will not 
be vitiated, as a correction may be easily made. 

