"At that speed, it must take a million miles of film before you get up steam."
"It would, if the film were being exposed. There is only about a hundred yards of film all told, which will run over these huge drums in an endless belt. There is a regular camera shutter working on an electric principle which remains closed. When the switch is tripped, the shutter opens in about two thirty-thousandths of a second, stays open just one one-hundredth of a second, and then closes. This time is enough to expose nearly all of our film. When we have our picture, I shut the current down, start applying a magnetic brake, and let it slow down. It takes over an hour to stop it without breaking the film. It sounds complicated, but it works all right."
"Where is your switch?"
"THAT is the trick part of it. It is a remote control affair. The shutter opens and starts the machine taking pictures when the back door of the paying teller's cage is opened half an inch. There is also a hand switch in the line that can be opened so that you can open the door without setting off the camera, if you wish. When the hand switch is closed and the door opened, this is what happens. The shutter on the camera opens, the machine takes five thousand pictures during the next hundredth of a second, and then the shutter closes. Those five thousand exposures will take about five minutes to show at the usual rate of sixteen per second."
"You said that you had to get plenty of light. How are you managing that?"
"The camera is equipped with a special lens ground out of rock crystal. This lens lets in ultra-violet light which the ordinary lens shuts out, and X-ray film is especially sensitive to ultra-violet light. In order to be sure that we get enough illumination, I will set up these two ultra-violet floodlights to illumine the cage. The teller will have to wear glasses to protect his eyes and he'll get well sunburned, but something has to be sacrificed to science, as Dr. Bird is always telling me."
"It's too deep for me," said Carnes with a sigh. "Can I do anything to help? The doctor told me to stand by and do anything I could."
"I might be able to use you a little if you can use tools," said Casey with a grin. "You can start bolting together that light proof shield if you want to."
"WELL, Carnes, did you have an instructive night?" asked Dr. Bird cheerfully as he entered the First National Bank at eight-thirty the next morning.
"I don't see that I did much good, Doctor. Casey would have had the machine ready on time anyway, and I'm no machinist."
"Well, frankly, Carnes, I didn't expect you to be of much help to him, but I did want you to see what Casey was doing, and a little of it was pretty heavy for him to handle alone. I suppose that everything is ready?"
"The motor reached full speed about fifteen minutes ago and Casey went out to get a cup of coffee. Would you mind telling me the object of the whole thing?"
"Not at all. I plan to make a permanent record of the work of the most ingenious bank robber in the world. I hope he keeps his word."
"What do you mean?"
"Three days ago when Sturtevant sweated a 'confession' out of poor Winston, the bank got a message that the robbery would be repeated this morning and dared them to prevent it. Rogers thought it was a hoax, but he telephoned me and I worked the Bureau men night and day to get my camera ready in time for him. I am afraid that I can't do much to prevent the robbery, but I may be able to take a picture of it and thus prevent other cases of a like nature."
"Was the warning written?"
"No. It was telephoned from a pay station in the loop district, and by the
