In the United Kingdom and Australia, a ceiling rose is a decorative element affixed to the ceiling from which a chandelier or light fitting is often suspended. They are typically round in shape and display a variety of ornamental designs.
In modern British wiring setups, light fittings usually use loop-in ceiling roses, which also include the functionality of a junction box.
According to Dan Cruikshank and Neil Burton in Life in the Georgian City, the use of gas lighting in the new House of Commons in 1852 must have reassured many people of its safety, and perhaps marked the turning point in public perception. In the cities where gas mains supply was available, many houses adopted gas lighting from the 1860s.
These early fittings used 'fishtail' and 'batwing' burners, which were relatively inefficient. The flame smoked badly and in the more impressive houses built at this time, huge ceiling roses were designed to conceal ventilation grilles which conducted the fumes to a vent in the outside wall.
(extract from http://www.buildingconservation.com/articles/light98/light98.htm)