It was a tedious process to drill through the steel of the outer casing of the safe and it was getting late.  I shut the door to the office so that Miss Wallace could not see.

At last by the cessation of the low hum of the boring, I knew that he had struck the inner lead lining.  Quietly I opened the door and stepped out.  He was injecting something from an hermetically sealed lead tube into the opening he had made and allowing it to run between the two linings of lead and steel.  Then using the tube itself he sealed the opening he had made and dabbed a little black over it.

Quickly he shoved the safe back, then around it concealed several small coils with wires also concealed and leading out through a window to a court.

“We’ll catch the fellow this time,” he remarked as he worked.  “If you ever have any idea, Walter, of going into the burglary business, it would be well to ascertain if the safes have any of these little selenium cells as suggested by my friend, Mr. Hammer, the inventor.  For by them an alarm can be given miles away the moment an intruder’s bull’s-eye falls on a hidden cell sensitive to light.”

While I was delegated to take Miss Wallace home, Kennedy made arrangements with a small shopkeeper on the ground floor of a building that backed up on the court for the use of his back room that night, and had already set up a bell actuated by a system of relays which the weak current from the selenium cells could operate.

It was not until nearly midnight that he was ready to leave the laboratory again, where he had been busily engaged in studying the tortoiseshell comb which Miss Wallace in her weakness had forgotten.

The little shopkeeper let us in sleepily and Kennedy deposited a large round package on a chair in the back of the shop, as well as a long piece of rubber tubing.  Nothing had happened so far.

As we waited the shopkeeper, now wide awake and not at all unconvinced that we were bent on some criminal operation, hung around.  Kennedy did not seem to care.  He drew from his pocket a little shiny brass instrument in a lead case, which looked like an abbreviated microscope.

“Look through it,” he said, handing it to me.

I looked and could see thousands of minute sparks.

“What is it?” I asked.

“A spinthariscope.  In that it is possible to watch the bombardment of the countless little corpuscles thrown off by radium, as they strike on the zinc blende crystal which forms the base.  When radium was originally discovered, the interest was merely in its curious properties, its power to emit invisible rays which penetrated solid substances and rendered things fluorescent, of expending energy without apparent loss.

“Then came the discovery,” he went on, “of its curative powers.  But the first results were not convincing.  Still, now that we know the reasons why radium may be dangerous and how to protect ourselves against them we know we possess one of the most wonderful of curative agencies.”