The old problem of utilizing the heat of the sun for the production of power has recently been revived in Italy, according to a Milan correspondent of "The Times" trade supplement. The idea of concentrating the sun's rays by means of large mirrors and lenses is not new, but, owing to the high cost of the plant and its low thermal efficiency, it so far has been little more than a scientific curiosity.
An Italian engineer has now put forward a scheme based on an entirely different principle. He proposes to use a turbine driven by the vapour of substances which vaporise at a low temperature, such as ammonia or sulphurous anhydrides. The turbine would be erected on the margin of a lake, and the ammonia or other sub-
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