had definitely as yet failed to appear.
The unambiguous experimental proofs of the correctness of the foregoing theoretical relation began with the publication of the accompanying photo-electric results[171] which were reported briefly in 1914, and submitted in extenso in September, 1915. These were in a form to prove the correctness of the Einstein equation; for monochromatic light of known frequency
fell upon a metal and the maximum energy of electronic ejection was found to be exactly determined by
as Einstein’s equation required.
A year or two later Duane1[172] and his associates had found unambiguous proof of the inverse effect. A target had been bombarded by electrons of known and constant energy
and the maximum frequency of the emitted ether waves (general
