Doctor," replied Carnes, "but I know you well enough to obey orders and to keep my mouth shut until it is my turn to speak."
Few men could resist Dr. Bird when he set out to make a favorable impression, and even a world's champion is apt to be flattered by the attention of one of the greatest scientists of his day, especially when that scientist has made an enviable reputation as an athlete in his college days and can talk the jargon of the champion's particular sport. Henry Ladd promptly capitulated to the charm of the doctor and allowed himself to be led away to supper at Bird's club. The supper passed off pleasantly, and when the doctor requested an interview with the young athlete in a private room, he gladly consented. They entered the room together, remained for an hour and a half, and then came out. The smile had left Ladd's face and he appeared nervous and distracted. The doctor talked cheerfully with him but kept a firm grip on his arm as they descended the stairs together. They entered a telephone booth where the doctor made several calls, and then descended to the street, where they entered a taxi.
"Maywood airdrome," the doctor told the driver.
TWO hours later the big Martin bomber which had carried the doctor to Chicago roared away into the night, and Bird turned back, reentered the taxi, and headed for the city alone.
When Carnes received the telephone call, which was one of those the doctor made from the booth in his club, he hurried over to the First National Bank. His badge secured him an entrance and he found Casey busily engaged in rigging up an elaborate piece of apparatus on one of the balconies where guards were normally stationed during banking hours.
"Dr. Bird said to tell you to keep on the job all night if necessary," he told Casey. "He thinks he will need your machine to-morrow."
"I'll have it ready to turn on the power at four A.M.," replied Casey.
Carnes watched him curiously for a while as he soldered together the electrical connections and assembled an apparatus which looked like a motion picture projector.
"What are you setting up?" he asked at length.
"It is a high speed motion picture camera," replied Casey, "with a telescopic lens. It is a piece of apparatus which Dr. Bird designed while he was in Washington last week and which I made from his sketches, using some apparatus we had on hand. It's a dandy, all right."
"What is special about it?"
"The speed. You know how fast an ordinary movie is taken, don't you? No? Well, it's sixteen exposures per second. The slow pictures are taken sometimes at a hundred and twenty-eight or two hundred and fifty-six exposures per second, and then shown at sixteen. This affair will take half a million pictures per second."
"I didn't know that a film would register with that short an exposure."
"THAT'S slow," replied Casey with a laugh. "It all depends on the light. The best flash-light powder gives a flash about one ten-thousandth of a second in duration, but that is by no means the speed limit of the film. The only trouble is enough light and sufficient shutter speed. Pictures have been taken by means of spark photography with an exposure of less than one three-millionth of a second. The whole secret of this machine lies in the shutter. This big disc with the slots in the edge is set up before the lens and run at such a speed that half a million slots per second pass before the lens. The film, which is sixteen millimeter X-ray film, travels behind the lens at a speed of nearly five miles per second. It has to be gradually worked up to this speed, and after the whole thing is set up, it takes it nearly four hours to get to full speed."
