The Great God Pan by Arthur Machen

Mr. Clarke, the gentleman chosen by Dr. Raymond to witness the strange experiment of the god Pan, was a person in whose character caution and curiosity were oddly mingled; in his sober moments he thought of the unusual and eccentric with undisguised aversion, and yet, deep in his heart, there was a wide-eyed inquisitiveness with respect to all the more recondite and esoteric elements in the nature of men. The latter tendency had prevailed when he accepted Raymond's invitation, for though his considered judgment had always repudiated the doctor's theories as the wildest nonsense, yet he secretly hugged a belief in fantasy, and would have rejoiced to see that belief confirmed. The horrors that he witnessed in the dreary laboratory were to a certain extent salutary; he was conscious of being involved in an affair not altogether reputable, and for many years afterwards he clung bravely to the commonplace, and rejected all occasions of occult investigation.

Indeed, on some homeopathic principle, he for some time attended the seances of distinguished mediums, hoping that the clumsy tricks of these gentlemen would make him altogether disgusted with mysticism of every kind, but the remedy, though caustic, was not efficacious. Clarke knew that he still pined for the unseen, and little by little, the old passion began to reassert itself, as the face of Mary, shuddering and convulsed with an unknown terror, faded slowly from his memory.