=“A Mechanical Bootblack.”=--A bootblacking apparatus is one of the latest developments of the nickel-in-the-slot machine, a specimen of which is undergoing trial in a French public garden. The customer drops his coin--in the present case a ten centime, or a two-and-a-half-cent piece--into the receptacle, which opens the way to a compartment where a brush cleans his boots; he next puts his feet into a second compartment and has them blackened; and then into a third, where they are polished. The operation takes about a minute and a half, and during the time the customer may watch the indications of its progress as they are shown upon the dial. The machinery working in the inside is very simple. An electric motor of small power--about eighteen kilogrammetres per second--controls the shaft on which the three rotary brushes are fixed, and the customer has only to unlock the machine, the same as all others of its kind, with his coin, and move the handle which opens the circuit and starts the motion. A representation of the machine at work is given in the accompanying illustration, for which we are indebted to _La Nature_. * * * * * =The “Barisal Guns.”=--A curious phenomenon of unexplained sounds like those of explosions, occasionally heard in different places over the earth, has attracted much attention, has been made the subject of a book recording several hundred accounts of it, by M. Ernest Van den Broeck, of Brussels, and has already been mentioned in the Popular Science Monthly. The phenomenon has been most carefully observed in India, where it seems to have assumed a peculiarly marked form, and is known there as the “Barisal guns.” M. Van den Broeck calls it “mistpoeffers,” or air-puffs. The most definite description of it is given in Nature by Mr. Henry S. Schurr, as he has heard it in India, where it has been observed over a wide range, but most clearly and frequently in the Baekergunge district, of which Barisal is the headquarters. The Barisal guns are heard most frequently from February to October, not during fine weather but just before, during, or immediately after heavy rain. They always sound in triplets--that is, three reports occur, one after another, at regular intervals--and though several guns may be heard, the number is always three or a multiple of three. Sometimes only one series of triplets of sounds is remarked in a day; at other times the author has counted as many as forty-five of them, one after another, without a pause. The report is exactly like the firing of big guns heard at a distance, except that it is always double, or has an echo. A number of conjectural solutions of the phenomenon have been put forth, but none of them accounts for it as a whole in any approaching a satisfactory manner. * * * * *