Jamieson, Fausset and Brown on Job 37:16

16. Hebrew, "Hast thou understanding of the balancings," &c., how the clouds are poised in the air, so that their watery gravity does not bring them to the earth? The condensed moisture, descending by gravity, meets a warmer temperature, which dissipates it into vapor (the tendency of which is to ascend) and so counteracts the descending force.

perfect in knowledge--God; not here in the sense that Elihu uses it of himself (Job 36:4).

dost thou know--how, &c.