The Dunwich Horror by H.P. Lovecraft

In the end the three men from Arkham -- old, white-bearded Dr. Armitage, stocky, iron-gray Professor Rice, and lean, youngish Dr. Morgan -- ascended the mountain alone. After much patient instruction regarding its focusing and use, they left the telescope with the frightened group that remained in the road; and as they climbed they were watched closely by those among whom the glass was passed around. It was hard going, and Armitage had to be helped more than once. High above the toiling group the great swath trembled as its hellish maker repassed with snail-like deliberateness. Then it was obvious that the pursuers were gaining.

Curtis Whateley -- of the undecayed branch -- was holding the telescope when the Arkham party detoured radically from the swath. He told the crowd that the men were evidently trying to get to a subordinate peak which overlooked the swath at a point considerably ahead of where the shrubbery was now bending. This, indeed, proved to be true; and the party were seen to gain the minor elevation only a short time after the invisible blasphemy had passed it.