his little sister , louisa , six months his junior , was , however , allowed to go to the market , and this was a source of great ranklement to the boy , as was the fact that louisa brought back from the market a glass globe , filled with speckles of light that glittered and flashed in the twilight , and which cast a warm and gentle radiance into the darkness of their bedroom in the farmhouse , while all tristran brought back from his relatives was a nasty case of the measles .