Published by Bell Telephone Laboratories, 1925
Seller: Sleepy Hollow Books, Huntington, VT, U.S.A.
Softcover. Condition: Good. Blue soft cover, black lettering, 3-hole punched. Science.
Published by The Institute Of Radio Engineers, No Place Noted, 1925
Seller: Any Amount of Books, London, United Kingdom
Soft cover. 8vo. pp 48. Original publisher's blue covers, lettered black on front cover. Illustrated in b/w throughout. Ownership signature of the aviation scientist, R. E. Gray (brother of Air Vice Marshall, J. A. Gray) on the front cover. Slight wear with hole punching at spine, otherwise about very good.