why does ahab take to the mast head on the second day of the chase?

Someone had yelled the whale was in sight, but no more was heard. Ahab then had himself pulled into the masts.

“Why sing ye not out for him, if ye see him?” cried Ahab, when, after the lapse of some minutes since the first cry, no more had been heard. “Sway me up, men; ye have been deceived; not Moby Dick casts one odd jet that way, and then disappears.”