He was made chief clerk in the Quartermaster office at the Presidio of San Francisco in 1883.

[3] Coleman is best remembered for his criticism of Helena Blavatsky and the claims of Theosophy.

He argued in his writings that Blavatsky had plagiarized her ideas from other sources and had stolen quotations.

[4][5][6] His article "The Sources of Madame Blavatsky's Writings" was published in an appendix to Vsevolod Solovyov's A Modern Priestess of Isis (1895).

Coleman demonstrated that Blavatsky's Isis Unveiled was largely plagiarized and included a list of the uncredited sources, including works by American orientalist Samuel Fales Dunlap.