Hi Eise
Here is a link to researching pre-WW1 soldiers -
http://www.nationalarchives.gov.uk/militaryhistory/army/step4.htmIf you cannot get to Kew, Findmypast are putting the main service papers online (by 2011). These are original documents in Kew (in series WO97). If you can get to Kew you firstly have to hope he was still serving in 1873. If he was discharged before then, then you need to know his regiment. Men discharged 1873 to 1882 are in fewer sections- infantry, cavalry, artillery, plus a few corps. Men discharged after 1883 are all together in alphabetical order.
If his papers do not survive, you can look in the Muster Books,
if you can discover his regiment.
Findmypast are also putting the Militia attestment papers (WO96) online as well in case he was not a Regular. I take it that he was at home, ie not in barracks? If you can find in in another census in barracks we can usually discover his regiment by the names of his officers.
Finding him on his children birth certificates may give his regiment.
Ken