Proceedings of the Boyal Society of Edinburgh. 195 



cronate, on the outside glaucous, within purple, edges scariose. Co- 

 rolla (li inch across) very handsome, of bright lilac colour; petals ob- 

 long, in the centre having an opaque linear stripe, which is glaucous 

 and 3-ribbed externally, internally of deep lilac, sides of clear and paler 

 lilac, and edges with long silky fringes of the same colour. Stamens 3, 

 bent to one side of the flower ; filaments short and colourless ; anthers 

 more than twice as long as the filaments, curved, having two slightly 

 divaricated yellow lobes at the base, above of a deep purple colour ; 

 pollen white, granules very minute. Pistil rather longer than the sta- 

 mens, curved in the opposite direction from them ; stigma minute, ter- 

 minal ; style subulate, grooved on three sides ; germen ovate, grooved ; 

 ovules 2 in each loculament. 

 This very beautiful species flowered at the garden of the Caledonian 

 Horticultural Society in May 1839, a plant having been obtained from 

 Messrs Veitch and Son, nurserj'men, Exeter, in the autumn previous. 

 It has grown in a mixture of peat and leaf-mould, and been kept in 

 stove heat, having been found elsewhere too tender for the greenhouse. 

 Its long succession of flowers will no doubt be developed during the 

 whole summer, each flower expanding betwixt 8 and 9 in the morning, 

 and in clear weather closing permanently about 2 p. m. 



Proceedings of the Poyal Society of Edinburgh, 



1839, January 21. — Lord Greenock Vice-President, in the 

 Chair. The following communications were read • — 



1. On the Colour of Steam under certain circumstances. By 

 Professor Forbes. 



The author accidentally remarked, that the colour of the Sun 

 seen tlirough vapour issuing from the safety-valve of a locomotive 

 engine is deep red, exactly similar to that which a column of smoke 

 or a smoked glass gives to it. 



He next noticed that this colorific character of steam extended 

 but a short way beyond the orifice, and that it gradually became 

 more opake, and perfectly white like noon-day clouds, both for 

 transmitted and reflected light. At moderate thicknesses, in this 

 state, its opacity is complete. 



These observations were fully confirmed by direct experiments 

 on high-pressure steam, made at Glasgow in December last. At 

 the moment of issuing from the steam-cock, it is perfectly trans- 

 parent and colourless ; at some distance from the orifice it becomes 

 transparent and orange-red ; but, still farther off, it is white, and 

 merely translucent. These properties were traced in steam from 

 a pressure above that of the atmosphere of 55 lb., down to an ex- 

 cess of only tiu-ee or four; and as in all cases the redness of the 

 transmitted light was more or less distinctly seen, (and an excess 

 of 10 or 15 lb. does as well as any higher pressure), it was con- 

 cluded that the effect of partial condensation in producing the phe- 

 nomenon, would be rendered visible in great thicknesses of vapour 

 of the lowest tension. 



The great analogy of the colour of steam to that which the 

 clouds assume at sunset, or distaut lights in certain conditions of 



