Page:Popular Mechanics 1928 11.pdf/27

 



To remove dead trees in burned-over areas, a portable electric power plant, drills and dynamite are being used successfully by forest rangers. Charges of the explosive, placed in holes drilled by electricity in the dead trunks, fell the tree much more rapidly than could be done by other methods and several can be destroyed at once. The dead trunk in a section that has been swept by fire, is considered one of the most dangerous menaces to other trees when a new fire occurs.

 

A new type of magneto, which has neither revolving armature, slip ring or distributor, is being marketed in England for marine engines. The magnetic field is produced by permanent bar magnets to which are attached pole pieces carrying the primary and secondary windings. An armature is at one end of the poles, and high-tension current is produced by pulling the armature away from the coils and breaking the primary circuit. The return of the armature closes the circuit and completes the cycle of operations. The intensity of the spark is entirely independent of the speed at which the engine is running. The mechanism for moving the armature is shaft-driven so the magneto can be fitted to existing engines without alteration.

¶ In proportion to the size of their bodies, insects have larger wings than birds.

