Unpublished manuscript, 'The sound vibrations of very high frequency produced by electric sparks' by Albert Campbell and D W [David William] Dye The authors write: 'An oscillatory spark discharge while it produces electrical waves, gives out at the same time intense, but usually inaudible, air or sound waves of high frequency.' Through a series of experiments at the National Physical Laboratory [London], they 'have lately succeeded in proving the existence of sound waves of much higher frequency than those mentioned, and have also measured their wave lengths'. Annotations in pencil throughout. Includes one page of photographs of experimental results. Subject: Physics / Electricity Received 5 December 1910. Read 8 December 1910. 3 December 1910