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twenty-four thousand parts of thoroughly dried clay, and was very uniformly distributed.

The report says: "In order to calculate, with some accuracy, the value of this body of wealth, we cut out blocks of the clay, and found, on an average, a cubic foot, as it lies in the ground, weighs one hundred and twenty pounds as near as may be. The assay gives seven-tenths grain, say three cents' worth, to the cubic foot. Assuming the data already given, we get four thousand one hundred and eighty million cubic feet of clay under our streets and houses, in which securely lies one hundred and twenty-six million dollars. And if, as is pretty certain, the corporate limits of the city would afford eight times this bulk of clay, we have more gold than has yet been brought, according to the statistics, from California and Australia."

Other calculations show that every time a load of clay is hauled out of a cellar enough gold goes with it to pay for the carting; and if the bricks which front our houses could have brought to their surface, in the form of gold leaf, the amount of gold which they contain, we should have a glittering show of two square inches on each brick. A single specimen of zinc proved to be absolutely free from gold.

These investigations proved that, while gold is justly considered one of the rarest metals, it is also one of the most widely diffused, and there are many philosophical reasons to be found in explanation of this apparent paradox.


IN 1880 I had the honor of lecturing before the Class of Science on the metamorphoses undergone by a drop of water, when I described the several phases of the grand cycle which the drop passes through from the moment it forms part of the great ocean mass till the time when after long journeys and numerous transformations it again joins its companions in the sea. A few months ago I in a similar way told the history of a grain of dust, dwelling especially on the universality and abundance of solid particles in the atmosphere, pervading everywhere on the surface of the earth.

I now proceed to describe the career of another minute body hundreds of times lighter than a drop of water or a solid corpuscle, confining myself to the consideration of its relations with

  1. Address before a public meeting of the Belgian Academy of Sciences, December 14, 1895.