For angel read ἀετοῦ eagle. Lit., one eagle. The eagle is a symbol of vengeance in Deu 28:49; Hos 8:1; Hab 1:8.
Mid heaven (μεσουρανήματι)
Only in Revelation, here, Rev 14:6; Rev 19:17. It means, properly, the meridian, the highest point in the heavens which the sun occupies at noon; not the space between heaven and earth.