George Underwood

“ From trials with an iron barometer in my possession, I think the long tube should be of one uniform bore throughout, and not larger at the vacuum end, as before recommended by me, unless made by the most careful and expert workman, since the difficulty of boring the latter, and the trouble of expelling air from it, become very great; while the scale also requires more than ordinary attention. ”

“ By inspection it will appear evident, that, turn the instrument as you will, the end of the long limb will be always immersed in mercury, and the contained air forced against the sides of the cistern. To keep the air in the cistern always in one part clear of the long or vacuum tube, if suspended in a box large enough to allow of its swinging freely on the hooks DD, no error will arise. The cistern end should always be carried uppermost in travelling or moving. ”