But--this was the maddening part of it--he had never been able to repeat the exact conditions; or, rather, to discover precisely what they were.

On that occasion he had entrusted one of his machines to his first cousin, Mary Porson, a big girl with her hair still down her back, rather idle in disposition, but very intelligent, when she chose.
Mary, for the most part, had been brought up at her father's house, close by.

Often, too, she stayed with her uncle for weeks at a stretch, so at that time Morris was as intimate with her as a man of eight and twenty usually is with a relative in her teens.
The arrangement on this particular occasion was that she should take the machine--or aerophone, as its inventor had named it--to her home.

The next morning, at the appointed hour, as Morris had often done before, he tried to effect communication, but without result.

On the following day, at the same hour, he tried again, when, to his astonishment, instantly the answer came back.