4 



THE POPULAR SCIENCE MONTHLY. 



cates its excess of heat by conductivity. 

 The luminous and ultra-violet rays produce 

 a similar effect ; but the motion which they 

 communicate to the molecules is distin- 

 guished by greater velocity, corresponding 

 to a higher temperature. Such an hypothe- 

 sis of molecular heating is sufficient to ex- 

 plain most of the effects produced by light 

 on bodies. The incandescence of the su- 

 perficial molecules, under the influence of 

 the most refrangible rays emanating from 

 a source at high temperature, must persist 

 for a finite time after the cessation of the 

 action of light. In this, perhaps, lies the 

 direct explanation of the phosphorescence 

 of short duration which M. Ed. Becquerel 

 has observed in nearly all solid bodies. 

 Fluorescence is also explained by the same 

 hypothesis, if we regard it as a phospho- 

 ivscence of short duration sufficiently in- 

 tense to be seen during the action of the 

 light. In general, moderate elevation of 

 temperature favors the reactions of combi- 

 nation, while in the highest temperatures 

 all known combinations undergo dissocia- 

 tion or decomposition. Thus, according to 

 M. Lermantoff s hypothesis, the less refran- 

 gible parts of the spectrum should produce 

 principally reactions of combination, and 

 the more refrangible parts decompositions. 

 This is precisely what M. Chastaing has 

 proved for the particular case of oxida- 

 tions. 



Metallic Anti-Resonators. It is known 

 that resonances in public halls can be modi- 

 fied or prevented by stretching wires across 

 the ceilings; and the principle has been 

 rudely applied in a number of instances with 

 fairly satisfactory results. Mr. A. C. Engler, 

 of London, has invented a plan for a sys- 

 tematic arrangement of steel plates, or 

 wires, which promises to accomplish the ob- 

 ject more completely. The effect of the 

 plates is to take up the most gentle vibra- 

 tions and greatly to increase the speed of 

 transmission. Wires have a similar prop- 

 erty, and are more convenient. In the most 

 advantageous application of Mr. Engler's 

 invention, one or more layers of steel wires 

 are stretched along the length of the room, 

 a few feet below the ceiling, connected by 

 cross-wires and spiral springs, and proper- 

 ly tuned, so that the vibration may be ab- 



sorbed and conveyed from one wire to an- 

 other, and instantaneously spread over the 

 whole building ; and the words of the speak- 

 er or the notes of the singer are so acceler- 

 ated that they reach the audience about 

 fifteen times more quickly than under 

 ordinary arrangements. The effeet is im- 

 proved and the tone enriched by using steel 

 plates. The system has been applied im- 

 perfectly, for the wires had to stop short of 

 the wall at one end in a lecture-room at 

 the South Kensington Museum of notori- 

 ously bad acoustic properties. Twenty-eight 

 lengths of steel wire were stretched across a 

 distance of sixty feet, and connected at the 

 end by steel-wire springs. Above them were 

 three other steel wires, connected with the 

 lower group, so as to form a perfect net- 

 work of wires. The effect was a complete dis- 

 tribution of the sound, so that a speaker at 

 the lecturer's table could be heard distinctly 

 in any part of the theatre, and all the acoustic 

 defects of the hall were considerably miti- 

 gated. 



Deeiinc of Country Population in Eng- 

 land. The returns of the new English cen- 

 sus show that the growth of the towns at 

 the expense of the rural villages and the 

 agricultural districts, which has been re- 

 marked in previous censuses, still con- 

 tinues ; and it is not certain that the 

 process of depletion of the country is not 

 progressive. The younger people are leav- 

 ing their rural homes so rapidly that in 

 some parts of the kingdom the difference 

 is sufficient to strike even casual travelers. 

 The causes of the decline of the agricultural 

 population are supposed to be attributable 

 partly to the increasing use of machinery, 

 which reduces the demand for hands ; partly 

 to reduction of wages ; but chiefly to an in- 

 crease in the dislike for agricultural labor 

 under existing conditions. The towns offer 

 better pay, more steady employment, better 

 protection from the weather, and more hope 

 of reaching an improved condition, than the 

 farms ; and work in towns, if it is hard, is 

 more lively and gregarious than agricultural 

 labor. The remedy suggested for the evil, 

 if one is to be applied, is peasant proprietor- 

 ship, under which the man who works may, 

 as on the Continent and in the United States, 

 feel that he is laboring for himself. 



