For such a current, the motion being horizontal, we have for all the circular elementary streams
H = p/G + v2/2g = constant;
∴ dH = dp/G + v dv/g = 0.
(7)
Consider two stream lines at radii r and r + dr (fig. 36). Then in (2), § 33, ρ = r and ds = dr,
v2 dr/gr + v dv/g = 0,
dv/v = −dr/r,
v ∞ 1/r,
(8)
precisely as in a radiating current; and hence the distribution of pressure is the same, and formulae 5 and 6 are applicable to this case.