POPULAR MISCELLANY. 



423 



by the farmer as the security to be offered. 

 In this way it comes to be the paramount 

 crop, and Httle chance is given for rotation 

 with other crops. 



Economy of Ligbti — In a paper before 

 the American Association, on the " Economy 

 of the Electric Light," Mr. A. Sterling stated 

 that, for lighting a compact block, the in- 

 candescent light could be regarded as not 

 more expensive than gas at $1.69 per thou- 

 sand. Mr. Preece stated that the same 

 quantity of gas gave more light when used 

 to work an engine than could be got from 

 it by burning it in the best gas-burners. 

 Instances were given during the discussion 

 where the amount of goods manufactured 

 had been increased, or the quality of the 

 goods improved, more than ten per cent, by 

 the introduction of electric lighting. Mr. 

 Preece explained the superiority of the elec- 

 tric light by showing that while in the arc- 

 light a candle - power was obtained by the 

 expenditure of one watt of energy, or in 

 the incandescent light of two and a half 

 watts, gas required the equivalent of sixty- 

 two and candles of ninety-seven watts, for 

 every candle - power produced. The most 

 formidable obstacle to universal electric 

 lighting was shown to be the great cost of 

 the mains for conveying the electricity over 

 long distances. 



Velocities of the Krakatoa Air- Wave. — 



Professor Tacchini has found by examina- 

 tion of the Richard barograph that slight 

 abrupt oscillations occurred in the baromet- 

 ric curves at Rome, on the 27th, 28th, and 

 29th of August, of last year, while the gen- 

 eral daily record of the pressure was not es- 

 sentially changed. Comparing the times at 

 which these oscillations took place with the 

 record of the times of the shocks at Kraka- 

 toa, he has deduced from them the conclusion 

 that the wave of the shocks reached Rome 

 from Krakatoa by the west, leaving the volca- 

 no at a velocity of 277 metres a second, while 

 the wave moving in the opposite direction 

 left it with a velocity of 296 metres. He 

 further calculated that the complete atmos- 

 pheric circuit round the globe was effected 

 by the east, leaving Rome at a velocity of 

 2£fe metres, and of 318 metres for the wave 

 going by the west. 



The Wind as a Land-Carver.— A paper 

 by General Prjevalski, on the structure of 

 the plateaus of Central Asia, suggests en- 

 larged views of the effects which atmospheric 

 agencies have had in modifying the forms of 

 mountains and valleys. Winds of excessive 

 violence seem to have caused the fragments 

 of stone to wear one upon another, and to 

 have ground them up into pebbles, gravels, 

 and sand ; then to have carried the lighter 

 parts of these materials to the valleys and 

 deposited them there as a loess which has 

 constantly grown thicker with succeeding 

 years and centuries. M. Alluard has re- 

 marked upon an accumulation of wind-de- 

 posits that seems to have taken place on the 

 Puy-de-Dome. A temple of Mercury of con- 

 siderable size formerly existed on the top 

 of that mountain, but it has been covered 

 up in the sand for nearly two thousand 

 years ; and, till some twenty or thirty years 

 ago, none of the visitors to the place could 

 have suspected that they were walking over 

 such a structure. 



Illnsory Memories, — A curious question 

 is presented by that experience of memory 

 which nearly every person has probably had, 

 in some form or degree, in which, when in- 

 troduced to a scene or event really new, we 

 have an impression, more or less distinct, 

 of having met it before. Professor Henry 

 L. Osborn, writing upon the phenomenon in 

 " Science," suggests that it may arise from 

 the dual structure of the brain, as the result 

 of imperfectly correlated action in two im- 

 ages or impressions not absolutely simulta- 

 neous. The latter impression, being a repe- 

 tition of the former one, gives rise to a 

 feeling that it has passed through the 

 mind at some indefinite previous time. Or, 

 the false or illusory memory may have a 

 real basis in some actual past representation 

 which is identical or closely similar to the 

 present one, or in some past images of the 

 waking imagination, or dream-life. Plato 

 conceived that these impressions gave sup- 

 port to the theory of a state of pre-existence 

 in which identical experiences may have 

 occurred. Mr. Sully suggests that the im- 

 pression may be an inherited recollection of 

 something that occurred to an ancestor. 

 Lewes and Ribot ascribe the illusions to a 

 false placing of a present mental image or 



