Page:Popular Mechanics 1928 11.pdf/9

 Thus the background does not merely appear to be bright, but actually is bright, though the glow from the lamps which have been turned off is not bright enough to detract from the light of those that are in circuit to form the picture. The net effect, however, is a much larger picture with infinitely more light than a neon lamp can produce, so it is possible to place a condensing lens in front of the lamp bank and project the picture on a screen. Jenkins is trying a similar system at the transmitting end, with 2,304 small photo-electric cells on which the image, focused by a lens, will fall.





Interesting stages in the hatching of crocodiles have been obtained by photography by training a camera on a number of eggs that were taken from a Java river bank and hatched in a laboratory under favorable conditions. One of the remarkable features of the young reptiles is their great development as they leave the shell, one specimen showing the naturally savage tendencies of the species by opening its jaws when a finger was moved close to it.



Stop your car or puncture your tires, is the forcible warning behind a mat of sharp spikes that can be spread across the road at a moment's notice to halt bandits traveling in automobiles or drivers of stolen cars. A press of a button expels the mat from its holder at the side of the street.

Mount Vesuvius, the world's most famous volcano, is approaching a new eruption, according to Professor Malladra, who operates the observatory on the mountain slope. The mountain's outbreaks occur from twenty to thirty years apart, and, as the last one of any size was in 1906, another is just about due. The conditions which give warning of an approaching eruption are the failure of springs around the mountain, a series of earthquake shocks, and the filling of the volcano crater with lava. The crater has been practically full since 1926, but the other two manifestations of approaching activity have not yet appeared. In each major eruption the stored-up energy in the mountain blows out the lava which clogs the crater and clears the volcano's throat, so it can "breathe" easier. Then the crater clogs up again and the process continues until the collected lava closes most of the vent and backs up pressure enough to cause another outbreak.

