Studied from its original page

Isobaric-isosteric unit-tubes (solenoid count)

equipotential-isopycnic unit-tubes (the companion pair of families) · unit-parallelograms

What it shows

Two families of lines over a slice of the atmosphere, spaced so that every small cell where they cross stands for the same amount.

Count the cells between two verticals, adding or subtracting each by the direction you go round: the count says how far the air is from balance.

See the original page — Fig. 17, full-page figure on unnumbered p. [102] (archive leaf n111)

Published 1910 (A) and both authors of Part I died before 1955 (Bjerknes 1951, Sandstrom 1947; B ended 2021 at the latest).

Built in 5 steps, as its maker described

section 72 'Unit-Tubes', pp. 120-121; section 73, pp. 121-122; Figs. 17, 18, 21, 24

Skeleton drawing, not the original plate

121 other forms share this skeleton

Attribution checked against the source