Dear Colleagues,
After extensive, yet unsuccessful, searching I am hoping the kalpavṛkṣa [which is this list] may entice someone to help me, or point me in the right direction, to access the following article:
Umesh, Mishra. "Physical Theory of Sound and its Origin in Indian Thought." AUSt 2, 1926, 229-290.
This article is referenced in both Harold Coward's Encyclopedia of Indian Philosophies Vol 5: Philosophy of the Grammarians pg. 537, and George Cardona's Pāṇini: A Survey of Research pg. 126.
With all best wishes,
Brian Campbell