They were delighted to know! The chance to see someone operating by daylight was too good to miss. They said a quick farewell to Belsely and hurried off across the field.
There was no one in sight as they crossed the picnic grounds, but when they climbed to the top of the hill and stood on the edge of the cornfield, they could see a man in khaki clothes bending over something between the rows of corn plants.
"Just what the ghosts were doing," Rick exclaimed. "Let's hurry and find out what he's up to!"
They walked swiftly down the rows of corn, making no attempt at concealment. This was a frontal attack. The stranger saw them coming and stood up.
Rick looked him over. The man was about forty, tanned and clean-shaven, with horn-rimmed glasses. Not at all a ghostly type.
The boys walked right up to the man and gave him a cordial hello, which the stranger returned.
"We couldn't help being curious," Rick said. "Do you mind if we watch?"
"Not at all." He indicated the open suitcase at his feet. It contained a built-in instrument with a meter and earphones. There was also a tubular attachment on the end of a thick wire.
Rick recognized it at once and a thrill shot through him. The stranger was somehow connected with the mystery.
"Isn't that a Geiger tube?" he asked.