  It is shown that a dilute property of an $\alpha$ particle condensate can be
seen in the Airy structure of nuclear rainbow and prerainbow scattering. The
dilute property of the Hoyle state of $^{12}$C with a developed $\alpha$
cluster structure is discussed by studying refractive $^3$He+$^{12}$C and
$\alpha$+$^{12}$C scattering.
