The author gave an account of a new, easy, and economical method of ascertaining the maximum and minimum of the oscillations of the barometer during the absence of the observer. It consists of two tubes, the diagonal and rectangular barometer of the author, fixed in the same frame. A piece of thick iron wire is introduced into the upper part of the former, and a similar piece into the horizontal arm of the latter. These pieces of wire are pushed before the mercurial columns, and when the mercury recedes, they remain behind, like the index in Rutherford's thermometer. That in the diagonal barometer will give the maximum, the wire in the rectangular barometer will indicate the minimum.