The Ray of Madness — S.P. Meek

"There's no hurry, Doctor," replied Operative Carnes of the United States Secret Service as he entered the room and sat on the edge of the Doctor's desk. "I haven't got a case up my sleeve this time; I just came in for a little chat."
"All right, glad to see you. Read that latest volume of the Zeitschrift for a while. That article of Von Beyer's has got me guessing, all right."
Carnes picked up the indicated volume and settled himself to read. The Doctor bent over his apparatus. Time and again he made minute adjustments and gave vent to muttered exclamations of annoyance at the results he obtained. Half an hour later he rose from his chair with a sigh and turned to his visitor.