The field of operations was now transferred to England, where, under the auspices of the British Association, four ascents were made by John Welsh of the Kew Observatory in the great _Nassau_ balloon managed by Green, the veteran aeronaut. The special object of these investigations, like those in France, was the determination of the temperature and hygrometric condition of the air at different elevations. Besides this, samples of air at different heights were collected for analysis and the light reflected from clouds was examined for polarization. Recognizing that on account of the calm prevailing in the car of the balloon and the great solar radiation, the readings of the thermometer would be affected, Welsh enclosed the thermometers in polished tubes through which air was forced by bellows. This was the first aspirated thermometer, which alone gives the true temperature of the air with the conditions prevailing in a balloon. The instrument fell into oblivion until a few years ago, and to this fact is due the fictitious temperatures generally obtained by aeronauts. Welsh reached heights of from 12,500 to 23,000 feet, and his observations showed that the temperature of the air decreased uniformly with height until at a certain elevation, varying on different days, the decrease is arrested, and for a space of 2000 or 3000 feet the temperature remains nearly constant, or even increases slightly; the regular diminution being afterwards resumed and generally maintained at a less rapid rate than in the lower air, and commencing from a higher temperature than would have existed but for the interruption. The variation of the decrease with the seasons was also demonstrated. The humidity did not change much with height, and it was nowhere very dry. Finally, the light of the clouds was proved not to be polarized, and the permanent composition of the atmosphere was confirmed.