POPULAR MISCELLANY. 



861 



photography. When we come to the other 

 end of the spectrum, the yellow and red, or 

 more refrangible rays, we find that they 

 promote the formation of chlorophyl and 

 so turn vegetation exposed to them green, 

 favoring the growth of green plants. In 

 this we may discover one of the purposes 

 which chlorophyl fills as that of a special 

 coloring - matter to the plant to filter out 

 the more injurious rays and protect the del- 

 icate protoplasmic cell-contents from their 

 destructive action. 



Healthy and Unhealthy Occupations. 



The English Registrar-General has made a 

 comparison between healthy and unhealthy 

 occupations. Assuming the normal average 

 death-rate of the community as the unit of 

 comparison, and calling it 1,000, particular 

 occupations may be regarded as healthy 

 or unhealthy according as the death-rates 

 among those pursuing them fall above or 

 below that figure. The most healthy occu- 

 pation appears to be that of ministers of 

 religion, whose rate is 556. Next are 

 gardeners and nurserymen, 599 ; farmers 

 and graziers, 631 ; agricultural laborers, 

 701 ; schoolmasters, 719 ; and grocers, coal- 

 merchants, paper, lace, and hosiery manu- 

 facturers, wheelwrights, ship-builders and 

 coal-miners, with all of whom the average 

 death-rate is under 775. The most un- 

 healthy occupations are the trades con- 

 nected with the liquor -traffic and hotel 

 service, with which the death-rate is 2,205 ; 

 following these are general laborers in 

 London, 2,020 ; costermongers, bankers, and 

 street sellers, 1,879 ; innkeepers, etc., 1,521 ; 

 and brewers, 1,361. After the trades con- 

 cerned with alcohol, the highest rates are 

 furnished by occupations that involve the 

 breathing of dust other than coal-dust 

 and exposure to lead-poisoning. The death- 

 rate among butchers is also high, 1,170. 



Cause of Thnnder. M. Him explains 

 thunder and the explosive noise of mete- 

 orites by observing that the air traversed by 

 an electric spark that is, a flash of light- 

 ning is suddenly raised to a very high tem- 

 perature, and has its volume considerably 

 increased. The column of gas thus sud- 

 denly heated and expanded is sometimes 

 several miles long ; as the duration of the 



flash is not even a millionth of a second, it 

 follows that the noise bursts forth at once 

 from the whole column ; but for an observer 

 in any given place, it begins when the light- 

 ning is at the least distance. In precise 

 terms, the beginning of the thunder-clap 

 gives us the minimum distance of the light- 

 ning, and its duration the length of the 

 column. The author points out that a bul- 

 let whistles in traversing the air, so that we 

 can to a certain extent follow its flight ; the 

 same thing happens with a falling meteorite 

 just before striking the earth. The noise 

 actually heard has been compared to the 

 flight of wild geese, or to the sound pro- 

 duced when one tears linen ; it is due to the 

 fact that the air, rapidly pushed on one side 

 in front of the projectile, whether bullet or 

 meteorite, quickly rushes back to fill the gap 

 left in the rear. The velocity of the mete- 

 orite is so great that the matter on its sur- 

 face will be torn away by the violence of the 

 gaseous friction produced, and will be vapor- 

 ized at the same time by the heat. This is 

 undoubtedly the origin of the smoke which 

 meteorites leave trailing behind them. With 

 this velocity the sound following the mete- 

 orite is vastly deeper and more like thunder 

 than that which attends the passage of the 

 relatively slow-going bullet. 



Prehistoric Chronology of America. 



Dr. D. G. Brinton, Vice-President of the An- 

 thropological Section of the American Asso- 

 ciation, gave there a " Review of the Data 

 for the Study of the Prehistoric Chronology 

 of America." The resemblances between 

 American legends and Oriental myths were 

 considered accidental. The annals of the 

 Mexicans, the Mayas of Yucatan, and the 

 Quichas of Peru, carry us back hardly more 

 than five hundred years. The recollections 

 of the more savage tribes did not extend back 

 more than two centuries. A calm weighing 

 of the testimony respecting the stone build- 

 ings of Mexico, Yucatan, and Peru, places 

 them all well within our own era, and most 

 of them within a few centuries of the dis- 

 covery. The much more ancient artificial 

 shell-heaps along the coasts furnish data to 

 prove that the land was inhabited several 

 thousand years ago. The industrial activity 

 of man in America may be traced by the re- 

 mains of his weapons, ornaments, and tools, 



