In number 11, of last volume, Scientific American, we illustrated and described the apparatus of M. Alexandre, for submarine diving and exploration, and without any doubt we consider it an ingenious apparatus. Since that time we have heard little about it, excepting some experiments made at the Brooklyn Navy Yard and at the Battery during the last Fair of the American Institute. In France, where it was invented, it is more highly esteemed. In the harbor ofCherbourg, which is occupied with docks and arsenals, one of these machines, 40 feet long, is employed daily to remove some submarine rocks which obstruct the entrance to one of the basins. It is of a large capacity, for nine men can go down in it and work for eight hours under Water, with the supply of air which they take down with them. There is no need of tubes and force pumps to supply pure air from above. In the description which we published on the page referred to, it is stated that lime water is employed to purify the atmosphere in the Explorer when it becomes impure by the carbonic acid gas expelled from the lungs of the operators. It has been found by experiment that when the apparatus is working in a current, there is not the least occasion for the lime water. The carbonic acid is heavier than 'the common atmosphere, and also combines more readily with water, therefore it - drops down into the current, in which the men work, at the,bottom of the' machine, and is carried off; this is an important scientific fact well worth treasuring up, as it proves to us that a vessel of water placed upon a stove answers more than one beneficial purpose, viz., to send moisture through the atmosphere ; it also absorbs impurities which may be in it. Running streams in cities and villages, upon the same principle, tend to promote health by absorbing impurities from the atmosphere, as well as carrying them off by mechanical contact.