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.

  • John Welsh
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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    stopcocks, from which the air had been exhausted. All the instruments which were at all liable to accident were supplied in duplicate. The construction of the meteo- rological instruments was confided by the Committee to Mr. P. Adie of London, under my own general superintendence. They were executed by him in a very satisfactory manner, having been made with much accuracy and with an anxious wish to promote the success of the experiments; many of the mechanical arrange- ments for the convenience of observation having also been devised by him. Barometers.—The barometer employed was of the siphon form, on the construc- tion generally known as Gay-Lussac’s. The tube was affixed to a brass scale in much the same way as a thermometer is attached to its scale. The brass scale was fixed within a stout rosewood frame furnished with a door which could be closed during carriage. The diameter of the tube was 0'25 inch. The graduation was made from the middle point upwards and downwards; each division being -2^th of an inch long, but representing twice that value; so that an observation of either branch of the siphon would give the length of the column of mercury, subject to a correction for inequality of the tube and error in the position of the zero-point of the scale. A complete observation of the instrument required however readings of both branches of the siphon, the true height of the mercury being the mean of the two. In order to facilitate rapidity of observation, verniers were dispensed with, the height of the mercury being merely estimated with reference to the scale placed behind it, just as if it had been a thermometer of large calibre. As it would have been nearly impossible to obtain in the car of the balloon a complete reading of both branches of the siphon for each observation, the corrections to the readings of the upper branch alone were previously obtained, throughout the anticipated range of the mercury, by the help of a large vacuum apparatus at the Kew Observatory, which has been employed in the pendulum experiments of Colonel Sabine and Professor Stokes. The barometers having been suspended within the receiver, the air was exhausted by about half an inch of pressure at a time, and readings taken from which tables of corrections were computed for different heights of the mercury. These corrections have been applied to all the observations. The difference between the indications of the siphon barometers and those of the Kew standard was also observed: both barometers were found to read 0'025 inch higher than the standard. It was found, by intercomparisons made last year, that the standard barometer at the Royal Ob- servatory, Greenwich, reads lower than the Kew standard by 0-003 inch. The balloon barometers thus read 0'028 inch higher than the Greenwich standard; and, as that barometer has been generally referred to in the computations of height, the equation +0-028 has been applied to the terrestrial observations to render them comparable with those of the balloon barometers. Each barometer was provided with a thermo- meter to indicate the temperature of the mercury. In order to obtain this tempe- rature more accurately, the bulb of the thermometer (which was cylindrical, about 1± inch long and |th of an inch diameter) was immersed in mercury contained in a
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