An account of meteorological observations in four balloon ascents : made under the direction of the Kew Observatory Committee of the British Association for the Advancement of Science / by John Welsh ; communicated by Colonel Sabine, by the request of the Council of the British Association for the Advancement of Science.

  • Welsh, John, 1824-1859.
Date:
1853
Catalogue details

Licence: Public Domain Mark

Credit: An account of meteorological observations in four balloon ascents : made under the direction of the Kew Observatory Committee of the British Association for the Advancement of Science / by John Welsh ; communicated by Colonel Sabine, by the request of the Council of the British Association for the Advancement of Science. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    tube of the same diameter as that of the barometer. The necessity for this precaution was found to be great, as very large differences sometimes existed between the tem- perature of the air thermometer and that of the mercury. Dry and Wet Thermometers.—Two pairs of dry and wet thermometers were employed. One pair was mounted with the bulbs protected from radiation by a double conical shade, having highly polished silver surfaces, open at top and bottom to allow the circulation of the air. The inner shade was 2 inches high, if inch wide at the lower, and half an inch at the upper end: the outer shade was also 2 inches high, 2f inches wide at the lower, and If inch at the upper end*. Both thermo- meters were furnished with shades exactly similar; the bulbs being thus in the same circumstances, and completely protected from direct radiation. The thermometers were supported, 3f inches apart, by the arms of a light brass frame, also with a polished silver surface. A small brass cistern was fixed near the wet thermometer, from which water was conveyed to the bulb by a conducting string of floss silk ; when however the temperature fell below the freezing-point, the string was cut away and the bulb occasionally dipped in water. As it was of essential importance that the thermometers should acquire with the utmost possible rapidity the temperature of the surrounding air, an arrangement was made, in connection with the second pair of dry and wet thermometers, for pro- ducing artificially a more rapid current over the bulbs than they would be exposed to by the mere vertical motion of the balloon. It was also thought desirable to avoid any tendency to a stagnation of the vapour of water in the neighbourhood of the wet bulb owing to the want of a sufficient circulation of air to carry it off, as might be the case when the balloon was nearly stationary or moving very slowly. An increased velocity in the circulation of the air would also tend to remove the effects of radia- tion, if the thermometers were not already sufficiently protected by the shades. With these objects the following contrivance was adopted. The thermometers were fixed vertically with their bulbs enclosed in two tubes placed side by side, and con- nected with each other by a cross tube joining their upper ends ; these tubes having silver surfaces, and being further protected by a silver shade of the same dimensions as the outer shade of the other pair of thermometers. The first tube, in which was the bulb of the dry thermometer, had at its lower end a communication with the air: by means of an aspirator a current was produced from this opening, upwards over the dry bulb, then passing, by the communication at the top, into the second tube down which it moved over the wet bulb, leaving it by an opening connected by a flexible pipe with the aspirator. By this means, the temperature of the air was deter- mined in its passage over the dry bulb, and afterwards its hygrometric condition on coming in contact with the wet; the vapour of water formed at the latter being car- ried off immediately into the aspirator. The whole distance which the air had to * It might have been preferable to make the inner shade cylindrical instead of conical, as the air would have circulated more freely. 2 t 2