We hope that Mr. Crookes's radiometer may be applied to
shame the London Gas Companies. In one of his experiment* on the force exerted by the light, he showed that a gas-flame gave out five and a half times as much force as the candle against whose effect it was balanced, but no doubt the chief part Of the force in the case of the gas was exerted by what is called "the dark heat,"—i.e., the heat whieh is separate from the light. The interposition of blue glass appears to reduce the force exerted by the light not much less than one-half, and most London gas burns naturally so blue that it might be mistaken for burning brimstone. Mr. Crookes should be engaged to test the gas of the Metropolis every week, as Professor Frankland tests the water of the various Water Companies, and so at last we might be able to write and read at night in London, without the double danger of head-ache and ophthalmia from the gross impurity of the material supplied.
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