CHAPTER VIII
The Old Tower
Rick tightened the last screw that held the searchlight-telescope unit to his camera and looked at it with satisfaction. "I should get a picture," he murmured. There were still quite a few unknown factors. He knew the theoretical power of the infrared searchlight, but only an actual test would tell whether it gave enough light for the rather slow infrared film emulsion. He was sure that it wouldn't give enough light at its extreme range of eight hundred yards. In all probability, he would not get an image on the film at a distance greater than two hundred.
It was a little strange to think in terms of light. True, infrared was light. But it was not visible to the human eye. The searchlight would cast no beam that could be seen, although anyone close to it would be able to see dimly the hot filament of the bulb.
Another unknown was the ability of the film emulsion to register the reflected infrared rays of his particular searchlight. The emulsion had been designed originally for infrared flash bulbs. The motion-picture film had been made at his special order. It was not a stock item. He wished Professor Gordon were at Spindrift. Gordon could have measured the wave length of the searchlight on the lab equipment. Rick wasn't skilled enough to use the delicate spectroscopic wave analyzer as yet and Hartson Brant was busy with a problem in the library and couldn't be disturbed. He hoped he would have a chance to ask his father before he tested the camera.
He rechecked the data that had come with the film and started to do some figuring.
Scotty came in just as the phone rang downstairs. Both boys waited expectantly, and in a moment Mrs. Brant called. "It's an out-of-town call, for either one of you."
"We'll take it up here, Mom," Rick called back. He and Scotty raced for the landing.
Scotty reached the phone first. "Hello?" He nodded at Rick. "It's Cap'n Mike."