Mild arch of promise! on the evening sky Thou shinest fair with many a lovely ray, Each in the other melting.

Southey’s address to the “arch of promise” (the rainbow) treats a natural phenomenon as a moral and emotional emblem. Set against an “evening sky,” the rainbow becomes a gentle, consoling sign—its light not harsh but “mild,” its colors “melting” into one another rather than clashing. The lines emphasize harmony, gradation, and reconciliation: distinct “rays” retain individuality yet blend into a unified whole. In Romantic fashion, the external scene mirrors inward feeling, suggesting hope after storm, peace after turmoil, and the possibility that disparate experiences or emotions can be integrated into a coherent, beautiful order.