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��Popular Science Monthly

��inboard by mechanical exhausters and in turn pumped overboard. Underneath the hull the exhaust is sprayed out and carried back to the propellers. If there are any bubbles left they are churned up by the propellers as by an egg-beater. Thus the betraying wake left by a train of air bubbles is to be eliminated.

The noise from oil engines under water, to which objection has been raised by naval ofhcers, is caused by a final ex- pansion of gas, after it leaves the cylin- ders, from a pressure of about fifty pounds down to atmospheric. This is

��one can say. The Nav>' is frankly inter- ested in the project, but, following the usual government policy, it prefers to adopt the system only after it has been completely developed by some private company. About $300,000 have been thus far spent on the system. Its promoters are unwilling to make any further sacrifices. Here we have a good example of the use of a Naval Advisory Board. The Neff system may not be perfect ; but it has assuredly commenda- ble features enough to justify the Board in carrying on the further development

���The llama of South America corresponds to the camel of the East as a beast of burden in the desert regions of the Andes

��accompanied by rapid sharp reports and a reverberating roar. In the Neff system it is claimed that the exhaust is silent, because the engine is exhausted into a condenser or a closed chamber from which it is drawn at a partial vacuum and discharged overboard at nearly the out- side water pressure. The remaining noises are due to the movements of the machine parts, such as the clicking of valves. AH this noise, it is claimed, may be reduced by proper regulation and ad- justment. In testifying before the Com- mittee on Naval Affairs of the House of Representatives, Mr. Neff pointed out what the Popular Scienxe Monthly has already shown — that the characteris- tic hum of an electric motor can be picked up at a distance of fifteen miles by micro- phones and that this hum is easily dis- tinguished from the vibration of engines. Hence there is just as much objection to the electric motor as to the Diesel engine under water.

Whether or not the Neff system will be adopted by the United States Na\y no

��with government funds. If private com- panies were to wait for inventors to sub- mit commercially perfect devices we would have no tungsten lamp, no harvesting machinery, no electric motor. All new inventions are crude. They must be regarded as material for de- velopment by laboratory' engineers. Not until the government assumes that at- titude are we likely to improve our fighting machinery.

Llamas as Powder- Carriers

IN the semi-desert Andes countries the llama is the general beast of burden, cor- responding to the camel in the Old World. The photograph shows a troop of these singular animals transporting American powder to an interior Bolivian mining district, far from any railroad. The llamas are heading for the Andean Mountain passes, led by a reliable old bellwether. Two or three gauchos (herdsmen) will manage a bunch of fifty or sixty animals; for the creatures give little or no trouble unless overloaded.

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