Eternal Spirit, Source of truth. T. Cotterill. [Assurance of Salvation desired.] Appeared in his Selection of Psalms & Hymns, &c, 1810, No. 66, in 5 stanzas of 4 lines, and entitled, "For a well grounded hope of Salvation," stanza ii. being based on J. Hart's "Bless'd Spirit of truth, Eternal God" (1759), stanza ii. It was repeated in all subsequent editions of his Selection. In modern hymn-books it usually reads, "Eternal Spirit, God of truth," as in Dr. Hatfield's Church Hymn Book, N. Y., 1872. In this form it is in extensive use in America. Its use in Great Britain is limited. Stanza iv. of this hymn is stanza iv. of the cento “Spirit of Truth, Thy grace impart," q.v.
--John Julian, Dictionary of Hymnology (1907)