Green’s Dictionary of Slang

1. ¼ pint (143ml) of gin.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.
1895		C. Crowe Aus. Sl. Dict. 71: Sensation, a drink of liquor.

2. (Aus.) a half glass of sherry.

1859		‘Drinks and Drinking in Aus.’ Town Talk 19 Mar. 547: A sensation ... Half a glass of sherry.
1941		Baker Popular Dict. Aus. Sl.
1955		N. Pulliam I Travelled a Lonely Land (1957) 238/2: sensation – a glass of sherry.