An account is given of a new weight barograph which resembles that of Sprung in principle but differs almost entirely in detail. Its mechanism is driven electrically, and provides not only a clear graphical trace of the pressure but a printed numerical record of its value every hour. The usefulness of this lies not so much in facilitating the abstraction of the data from the charts as in adding materially to the accuracy, for changes in humidity have a decided effect on the width of the paper, and may under extreme conditions cause an error of a millibar in the trace.
The barometric tube and a counterweight hang from the ends of a beam, pivoted a t its centre, and on the beam is a rolling weight; when the beam is slightly tilted by a change of pressure a contact is made which through a sensitive relay brings into operation an electric motor. This moves the rolling weight until equilibrium is again reached and the position of the rolling weight controls both the trace and the number printed.
After a discussion of the fundamental principles the mode of construction is described in some detail, and finally the methods of adjustment and the compensation for temperature.