Thoreau writes in his journal:
  I am surprised to see over Walden Pond, which is covered with puddles, that seething or shimmering in the air which is observed over the fields in a warm day in summer, close over the ice for several feet in height, notwithstanding that the sky is completely overcast . . . It is so warm that I am obliged to take off my greatcoat and carry it on my arm . . .
