But, if such was the case, he sent back no answering signal, as was his invariable custom, when that of his friend reached him. Fred listened long and attentively, but caught no reply."I guess I'll have to try it again," he added, with a mingled laugh and shudder. "I think these walls can stand a little more such serenading."He threw his whole soul in the effort, and the screeching whistle that he sent out was frightful, followed, as it was, by the innumerable echoes. It seemed as if the walls took up the wave of sound as if it were a foot-ball and hurled it back and forth, from side to side, and up and down, in furious sport. The dread of losing his torch alone prevented the lad from throwing it down and clapping his hands to his ears, to shut out the horrid din. Some of the distant echoes, coming in after the others were exhausted, gave an odd, dropping character to the volley