My pleasure. The guys over there were also excited to see a quite rare photo of a gendarmes' general. In the meantime, brace yourself for further details on your great-grandfather:
He graduated from the same Pavlovskoye Officer School in Petersburg as his son thirty-some years later - which makes sense since it was customary for an officer's son to enroll in the same school as his father - and began his military service at 3rd Elisavetgrad Hussar regiment, then stationed at Zolotonosha, near Kharkov. In 1874 he retired and led a civil life until 1883, when he returned to the active service, this time at the Corps of Gendarmes. He was subsequently promoted and eventually became Major-General in 1907. In the same year he was appointed chief of Don regional headquarters of the Corps of Gendarmes [after holding similar offices in various regions: Kovna (which is in Lithuania), Yaroslavl, Poltava and Olonets] and served in such capacity until his final retirement in 1913, at which he was promoted to Lieutenant-General (Ret.). As of 1917, he lived in Petrograd at 13, Tverskaya St. (a rather upscale neighborhood I must say).