VOL. XLVII.] PHILOSOPHICAL TRANSACTIONS. 18? 



not found spontaneous in higher latitudes than the southern parts of France. 

 Dr. Stednian's description demonstrates likewise that the above plant was the 

 hyoscyamus nigcr, as he says, that ' it is known by its duskish bell-flower.' The 

 flower of black henbane is of that hue, being of a yellow colour interspersed with 

 veins of purple ; whereas the flower of the white henbane is of a pale yellow 

 colour. This error arises from the improper denomination imposed on many 

 plants by the ancients, and which has been preserved even since the revival of 

 letters ; which, to one not very well acquainted with botany, is liable to mislead. 

 Thus, in the case before us, the leaves of the black henbane are very little less 

 white than those of the white ; but this denomination took its rise from the difr 

 ferent colour of their seeds. In such cases therefore, without being well ac- 

 quainted with the specific difference of each plant, before it ripens its seed, it is 

 not a little difficult to distinguish them one from the other. This specific dif- 

 ference will be best furnished by the leaves. Thus in the henbane, the leaves of 

 the white are placed on long footstalks ; those of the black have none, but the 

 lower extremity of the leaf surrounds the stalk. 



XXIX. The best Proportions for Steam-engine Cylinders, of a Given Content, 

 considered. By Francis Blake * Esq. F.R.S. p. 197. 



The steam-engine, for draining of mines, is a master-piece of machinery, a 

 very capital contrivance in the works of art, and meriting our attention for fur- 

 ther improvements. The prodigious vessel of water to be kept always boiling, 

 when only an inconsiderable part of it is employed in the work, savours too little 

 of the frugality of nature, which we ought ever to imitate. But waving that 

 now, what Mr. B. inquires into here, and endeavours to regulate, is the propor- 

 tion of the cylinder's altitude and base ; which has not been hitherto noticed. 



It is evident, in the first place, from a general law of mechanics, that the 

 content of the cylinder remaining the same, the quantity of water discharged at 

 each lift will in all cases be equal, by only changing the distance of the centre 

 of the piston from the fulcrum of the balance. It will be granted also that the 

 excess of the column of atmosphere, above that of the water, is a weight on the 

 piston, driving it to a depth of about 5 feet, by the present construction, within the 

 cylinder ; acceleratedly till friction and an impediment from the steam, which 

 remains in the cylinder even after the jet d'eau, and is increased in elasticity 

 while its bounds are diminished, shall equal the accelerative force ; and that then 

 again the piston is retarded the rest of the way. It may be convenient to re- 



* Francis Blake, Esq. a gentleman of great fortune, and a very learned map, was the father of tl|e 

 present Sir Francis Blake, Bart, of Twizel Castle in the county of Northunjberland, also a learned 

 and very respectable characier. . , ,5^"" 4 



B B 2 



