some unknown point in the tube, and to remove the obstruction it was desirable to locate its position as closely as possible before digging down to the pipe. This was satisfactorily accomplished by firing a pistol at one end of the tube; its report was echoed from the obstruction, and indicated its position by the time required for the transmission of the sound. The pistol was fired in a hole in the side of the pneumatic tube near the end, which was capped and had a rubber-hose connection to the recording apparatus. The end of the rubber hose terminated in a chamber closed by a diaphragm about five inches in diameter, which had a stylus attached to it. A cock in the middle of the rubber hose was partly closed to reduce the force of the explosion on the diaphragm, and the pistol was fired. The sound-wave immediately produced a movement of the diaphragm, causing the stylus to make a mark on the record diagram. The hose cock was then fully opened, and when the sound-wave had traveled to the obstruction and been reflected back it again moved the diaphragm, and caused the stylus to make a second mark on the diagram. The lapse of time had been automatically recorded on the same diagram, so to determine the distance it was only necessary to note the exact interval of time between the direct and reflected reports, divide it by two, and multiply the quotient by the velocity of sound under the existing conditions." The obstruction was indicated at 1,537 feet from the diaphragm. Excavations were made at this place, and the carrier was found nearly at the calculated point. The limits of distance at which this method is applicable have not yet been determined, but Mr. Batcheller, the engineer of the Pneumatic Tube Company and the deviser of the above ingenious expedient, has found that in a tube 43.3 inches in diameter a pistol shot will vibrate a sensitive diaphragm at a distance of 65,129 feet; decreasing the diameter of the tube decreases the distance over which the pistol shot will act.
Diseased Meat in Paris.—The police of Paris, says the Lancet, have just laid hands on a vast fraudulent organization for evading the precautionary measures drawn up by the authorities for inspecting the meat distributed for consumption in the suburbs of Paris. Both for Paris and the suburbs all animals destined for food have to be killed in public slaughterhouses, where the strictest watch is kept by the municipal veterinary surgeons, who forbid the delivery to the butchers of any meat which exhibits the slightest suspicious signs. Elaborate regulations have been laid down as to the various diseases which render meat unfit for the food of man, and naturally enough tuberculosis is the complaint most rigorously watched for. The swindlers who have been arrested made up a vast organization which used to buy up from the farms of the eastern provinces and even in Germany such animals as, owing to disease, would have been refused for slaughter at the abattoirs, and, moreover, they bought them dirt cheap. These animals were then conveyed in regular herds to a small place near Paris and killed in sheds built at the bottom of an old quarry. Under cover of night the meat was taken away by the accomplice butchers and resold in the various suburban shops. In connection with this clandestine slaughterhouse the firm had a kind of cemetery, where those animals were buried the meat of which was too bad for even the swindlers to risk its sale in the market. Ivry was the place where the fraud was discovered, and the official inquiry shows that the organization was singularly complete. It is extraordinary that the slaughterhouse, which was in full work, should never have attracted the attention of the villagers, but it must be remembered that all killing was done by night and that the slaughtermen were all Germans who did not understand a word of French, and were therefore unable to engage in imprudent conversation with the neighbors.
How Aluminum is made.—In a paper read before the Manchester Junior Electrical Engineers, J. H. Henderson describes the two commercial methods of making aluminum: The agent which has made aluminum a commercial product is electricity. This is how electrolysis produces it (by one successful method): In a metal, carbon-lined crucible having two carbon electrodes, one of which acts as anode and the other as
