Before revision: It worked by complicated thin film surface effects, so scientists of the time didn't understand how it worked, except for a vague idea that radio wave detection depended on some mysterious property of "imperfect" electrical contacts.
After revision: It worked by complicated thin film surface effects, so scientists of the time did not understand how it worked, except for a vague idea that radio wave detection depended on some mysterious property of "imperfect" electrical contacts.