Page:Proceedings of the Royal Society of London Vol 1.djvu/252

Rh mountains or in the open sea. Hence it follows, that the mercury ought to stand somewhat higher when such a wind blows than with the same wind when it meets with no obstruction; and the more direct it blows upon the coast, and the higher the land is, the higher ought the mercury to rise. On the other hand, when the wind comes from oil” the bills, this dense air will be displaced; and thus the air over the coast will resume its natural state with a land wind.

Capt. Flinders concludes his paper with some general remarks upon the barometer, of which the following seem to be the most material :

It is not so much the absolute as the relative height of the mercury, and its state of rising and falling, that are to be attended to in forming a judgement of the weather.

In the open sea, the changes in the weather, and in the strength of the wind, appear to be the causes that chieﬂy aﬁ'ect the barometer; but, near the shore, a change in the direction of the wind seems to affect it as much, or more, than either of those causes taken singly.

On the open sea, also, the mercury seems to stand higher in a steady breeze of several days’ continuance, provided it does not blow hard, than when the wind is variable. Perhaps it is on this account, as well as from the direction of the Wind, that the mercury stands higher within the tropics than in those parallels where the winds are variable.

Upon the whole, our author thinks the barometer capable of af- fording so much assistance to the commander of a ship, that no com- mander in a long voyage should be without one.

The minium here described by Mr. Smithson was found disseminated in a compact carbonate of zinc. Its general appearance was pulverulent; but when a lens was used, it showed, in some places, a ﬂaky and crystalline texture. lts colour was the same as that of factitious minium: when gently heated by the blowpipe it became more obscure, but returned1 upon cooling, to its original colour. By a stronger heat it melted into litharge; and, upon charcoal, was reduced to lead.

In dilute nitric acid it assumed a coffee-colour; and on the addition of a little sugar, this brown calx was dissolved, producing a colourless solution. Upon being put into muriatic acid, with a little leaf-gold, the gold was soon entirely dissolved.

When it Was inclosed in a small bottle with muriatic acid, and a small piece of turnsole paper was ﬁxed to the cork, the paper in a short time entirely lost its blue colour, and became white. Even a slip of common blue paper, whose colouring matter is indigo, when placed in the above situation, underwent the same change.

This native minium, Mr. Smithson says, seems to be produced by