Midpoints & the 90° dial
Alfred Witte's Hamburg School and Reinhold Ebertin's Cosmobiology (Germany, 1920s–40s)
Alfred Witte and the Hamburg School made the midpoint — the point halfway between two planets — into a system; Witte's Regelwerk für Planetenbilder (manuscript 1928, published 1929) was the first systematic midpoint delineation, and he had coined the term 'half-sum' in a 1923 essay. Reinhold Ebertin distilled this into Cosmobiology (Kombination der Gestirneinflüsse, 1940), working with the 90° dial that Ludwig Rudolph built in 1931. Half-sums themselves are far older — they appear in Ptolemy, in the Lots, and in Bonatti — so Witte's real innovation was the interpretation, not the arithmetic.
What it measures
A midpoint is the shorter-arc halfway point between two bodies; a third body conjunct, square or opposite it — folded onto a 90° dial, where those three angles coincide — completes the picture. The midpoint tree lists every such contact.
Where practitioners disagree
- How tight an orb on the dial?
1.5° (Ebertin) or tighter
Ebertin's 1.5° is the standard cosmobiology orb for a direct midpoint contact.
This engine: 1.5° for midpoint contacts (Ebertin's convention).
Sources
- Alfred Witte, Regelwerk für Planetenbilder (1929)
- Reinhold Ebertin, Kombination der Gestirneinflüsse (Cosmobiology) (1940)