"it shocked him to feel at Stradbrook the greasy leather of harness."

This quote refers to a horse harness, a type of horse tack that allows a horse or other equine to pull vehicles such as a carriage, wagon or sleigh. Harnesses may also be used to hitch animals to other loads such as a plough or canal boat.

Horse Harness Closeup
Creative Commons AttributionHorse Harness Closeup - Credit: Pete Markham

 Stradbrook is an area in Dublin.