Off-print "from the Proceedings of the Royal Society, Vol. 44" for April 12, 1888. Autograph presentation copy from Lockyer to Dr. T. Sterry Hunt (see notes below). Illustrated with diagrams and spectra, including one folding plate. Original khaki-tan acidic wrappers detached and much cracked and chipped around edges and along spine, especially on rear panel; several numerical sequences pencilled/inked in tiny hand on rear wrapper; margins dusty and toned. Contents tanned, but clean and crisp. Although the contents are near fine, because of the detached covers a good copy only.