Father. They prevail in several parts of the Eastern and Southern Oceans, and evidently depend on the sun; for when the apparent motion of that body is north of the equator, that is, from the end of March to the same period in September, the wind sets in from the south-west; and the remainder of the year, while the sun is south of the equator, the wind blows from the north-east. These are called the monsoons, or shifting trade-winds, and are of considerable importance to those who make voyages to the East Indies.

Charles. Do these changes take place suddenly?

Father. No: some days before and after the change there are calms, variable winds, and frequently the most violent storms.

On the greater part of the coasts

I imagine, that it was neither pure gold nor pure silver.

Charles. But how could he discover the proportions of each metal? Father. I believe we have no other facts to carry us farther into the history of this interesting experiment. But to-morrow I will endeavour to explain and illustrate the matter.

CONVERSATION XV..

Of the methods of obtaining the Specific Gravity of Bodies.

EMMA. I am eager, papa, to claim your promise of describing the method of detecting the proportion of each metal, when two are mixed together in one mass.

Father. Suppose I take in change a guinea, which I suppose to be bad: upon trying it I find it weighs 129 grains, which is the standard weight of a guinea. I then weigh it in water, and it loses of its weight 84 grains, by which I divide the 129, and the quotient is 15.6, the specific

in a certain direction, and another in a contrary one; that is, the higher clouds will be moving perhaps north or east, while the weather-cock stands directly south or west. In cases of

this kind a sudden rarefaction must have taken place in the regions of one set of these clouds, and consequently the equilibrium is destroyed. This phenomenon is frequently found to precede a thunder storm; from which it has been supposed that the electric fluid is, in this and such like instances, the principal cause in producing the wind; and if in the more remarkable appearance we are able to trace the operating cause, we may naturally infer that those which are less so, but of the same nature, depend on a like principle.

Emma. Violent storms must be occasioned by sudden and tremendous

"gold." I will propose you an example.

What are the proportions of silver and gold in a guinea weighing 129 grains, whose specific gravity is found to be only 13.09; supposing the loss of standard gold 7.25, and that of a piece of siver, equal in weight to a guinea, 12.45, and the loss of the compound 9.85?

Charles. I first subtract the loss of standard gold 7.25 from the loss of the compound 9.85, the remainder is 2.6 I now take the loss of the compound 9.85, from that sustained by the silver, 12.45, and the remainder is also 2.6.

Father. Then the proportions of silver and gold are equal to one another, consequently the false guinea is half standard gold and half silver.

Here is another counterfeit guinea,