Abstract
THE subject is so old and well-worn that it is impossible to add anything new to it, still it is so large that there is no fear of its being exhausted by the few following notes. It will be going back quite far enough if we begin with Hook (Phil. Trans. i., 218, 1666), who invented the wheel barometer, and point out that his (1666) method consisted in using a mercury trough formed of two short open cylinders communicating near the bottom). Into one of these the lower end of the barometer tube was inserted while the float connected with the index rested on the mercury in the other. Derham (Phil. Trans. xx., 45, 1698), avoided the uncertainty caused by the float, cord, and index-bearings, and took his readings by means of a rod (terminating in a point) connected with the index by a rack and pinion. Gray (Phil. Trans. xx, 176, 1698) in the same year proposed the very method that is now in use for taking observations with the standard barometers, for he left the barometer tube free of all fittings and attachments, and read off the actual height of the mercurial column by means of a microscope (sic) sliding on a vertical scale. Fitzgerald (Phil. Trans. lii, 146, 1761) attached two movable indexes to the dial of the wheel barometer to show the highest and lowest points reached during any given period; and he also gave the float nearly the full range by having the upper part of the tube three inches in diameter, while the short upturned end was only half an inch diameter. In 1770 (Phil. Trans. lx., 74) he increased the range of the index by introducing a system of levers with arms of unequal length.
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BROWN, J. Barometers . Nature 26, 282–284 (1882). https://doi.org/10.1038/026282a0
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DOI: https://doi.org/10.1038/026282a0