In 1891, on the 5th of April, when the census was taken in Wales, Henry Ball, age 27, was found to be living with his parents, William and Charlotte, in Penarth. They resided at 54 Windsor Road as shown on this Google map:
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Both father and son are listed as "dairyman". A dairyman could be a worker or owner of a dairy farm or a seller of dairy products. Given that Henry was living with his father in town, I suspect their dairy business was the latter - seller of dairy products. Knowing that older brother John was farming in St. Andrews Major, I suspect that Henry and William may have sold milk and other products from John's farm and perhaps others. Did they have a formal business? How successful were they? Alas, more clues to discover..