Vacuum ][]rake.--The engineers of the French Northern Railway have made satisfactory experiments with the vacuum brake. MM. Sartiaux and Lartique have devised some ingenious arrangements for bringing it into automatic action, if any mistake is made respecting the crossings. Distressed passengers, who need help, can operate the brake instead of ringing a bell.--Nature.
C.
An African Sea.--A writer in the Scientific American has lately estimated the amount of evaporation from the surface of the proposed Algerian Sea, the reduction of the ocean level, and the time required to fill the sea with a bed of salt. In his calculations he seems to have omitted any consideration of the amount of vapor that would be recondensed, over the sea or in the neighborhood of its banks, so as to find its way back into the reservoir from which it was drawn. The elem'ents involved in the question are too numerous to be determined by a few ingenious numerical calculations, and the discussions in the French Academy show that there is no lack of able engineers and physicists, who are thoroughly competent and willing to look at the project in all its climatic and economical bearings, before any final decision is made.--Comptes Rendus. C.