Perceive its gentle rise.
Other forms are a2 b a3 b2, a4 b a5 b4, a5 b a4 b5 (cf. Metrik, ii, § 326).
Three isometrical verses and one shorter or longer end-verse can also be so connected, as e.g. on the scheme a b a4 b2 in Pope, Ode on Solitude (p. 45):
Happy the man whose wish and care
A few paternal acres bound,
Content to breathe his native air,
In his own ground;
or in Cowper on the model a b a4 b5 in Divine Love endures no Rival (p. 418):
Love is the Lord whom I obey,
Whose will transported I perform;