JrxE 14, 1895.] 



SCIENCE. 



(355 



pulilic lecture on Tlimsday evening the 

 IGtli inst., iu couueetiou with the Royal 

 Society's meeting. Prof. Cox has a gift too 

 rare with men of science, and most precious 

 to him whose chosen path of research leads 

 him into selve ogctire of abstruse problems 

 where for the many no light shines — the 

 gift of clear and eloquent exposition. His 

 subject was ■ Unsolved Problems in The 

 Manufacture of Light," and, in order to illus- 

 trate it worthily, he had brought with him 

 from Montreal the admirable apparatus of 

 his laboratory necessary for a series of exper- 

 iments and lantern views. He was assisted 

 by Messrs Barnes and Pitcher, and the large 

 and cultivated audience gathered in the 

 hall of the Xormal School listened enrap- 

 tured as he made plain mysteries that most 

 of them had regarded as impenetrable. 

 After referring to the time-honored sources 

 of light — the candle, oil lamp, gas, Auer 

 light, and the lime light — and showing that 

 each consisted in heating something till it 

 was incandescent, the lectui'er pointed out 

 that none of these gave an efficiencj' of more 

 than one per cent., the only scientific sys- 

 tems of combustion being the Auer light 

 and lime light. The modern method of elec- 

 tric lighting dated from Sir Humphi-ey 

 Davy's first production of the arc, with a 

 battery of 2,000 cells. The current thus 

 produced was still ample to heat refractory 

 substances to incandescence, but as zinc and 

 acid were many times as expensive as coal 

 and air the light could not come into prac- 

 tical use until the invention of the dj-namo 

 forty years afterward. "With the dynamo 

 the modern sy.stem was completed, and con- 

 sisted of three stages — the steam-engine, the 

 dynamo and the lamp. The purpose of 

 the lecture was to .show that in the steam- 

 engine and the lamp there is still an enor- 

 mous waste. After pointing out that light 

 was not created but was produced by the 

 conversion of energy, and explaining the 

 nature of energy as stored up in coal. Prof 



Cox dealt with the three stages in detail. 

 " The conversion of the coal-energy into the 

 mechanical energy," he said, '■ is of course 

 effected by the steam-engine, but in practice 

 not more than from 7 to 10 per cent, of the 

 energj- stored in the coal can be extracted by 

 the steam-engine, and theoretical considera- 

 tions fix an absolute limit to the perfection of 

 the steam-engine, showing that we can never 

 hope to convert so much as 30 per cent, of 

 the energj^ of coal by anj- form of heat- 

 engine. This is one unsolved problem iu 

 the manufacture of light — unsolved but still 

 capable of solution if some means of extract- 

 ing energj' from coal otherwise than by heat, 

 and more like the methods used in burning 

 zinc in a batteiy, can be discovered. At 

 present we are recklessly wasting our coal 

 supplies, and posteritj- will have a serious 

 grievance against us for squandering these 

 priceless stores.'' 



In the second stage of the process, the 

 dynamo, though so recentlj* invented, is 

 already nearly perfect, and scarcely any 

 energy is lost in its conversion by the 

 djTiamo into an electrical current. "We 

 reach the third stage, that is, the lamp, 

 with some 7 percent, of the original energy 

 still available. The lecturer here showed 

 a number of interesting experiments to 

 prove that the only form of energy useful 

 in producing vision consisted of a short 

 series of verj' minute waves, ranging from 

 the forty-thousandth to the sixty-thous- 

 andth of an inch in length, and that to pro- 

 duce these our only means at present was 

 to heat the molecules of some substance, 

 whereby we were compelled to waste the 

 gi-eater part of our efforts in producing heat, 

 which was worse than useless, before we ob- 

 tained the luminous rays. " Here then," 

 said Professor Cox, " is the second unsolved 

 problem, since even in the incandescent 

 lamp and the arc lamp not more than from 

 three to five per cent, of the energy supplied 

 is converted into light. Thus, of the original 



