NATURAL PHILOSOPHY. 135 



transmitted ray, which it directs to the NicoPs prism, serving as 

 anal^'zer. — Chemical News. 



SOURCE OF LIGHT IN FLAMES. 



According to Prof. Frankland, the light of a gas flame, and of 

 luminous flames in general, is not due, as has been generally 

 believed since the time of Sir Humphry Davy, to the presence of 

 solid particles. There are many flames possessing a high degree 

 of luminosity which cannot possibly contain solid particles, — as 

 the flame of metallic arsenic burning in oxygen, — or of carbonic 

 disulphide vapor in oxygen, or nitric oxide gas, or of phosphorus 

 in oxygen. He believes that the luminosity of these flames is due 

 to radiations from dense but transparent hydrocarbon vapors, when 

 carbon is present. 



THE ELECTRIC LIGHT. 



According to M. Felix Lucas, the luminous distance at which 

 the electric spark is visible is greater than that of a permanent 

 light, the apparent intensity of which would be 250,000 times that 

 of the spark. The light actually employed in modern light-houses 

 gives a brilliancy equal to 125 carcel lamps. An electric spark 

 possessing the illuminating power of the two-hundredth part only of 

 a carcel burner is superior in its power of projecting light, showing 

 the advantage of a warning light composed of intermittent flashes 

 of the electric spark from a powerful Leyden battery. He stated 

 that, in a laboratory experiment, 2 apparatuses were established, 

 1 voltaic battery equal to 125 carcel lamps, and a spark bat- 

 tery equivalent to only the one-two-thousandth part of a carcel 

 lamp; the photometer showed a marked superiority in favor of the 

 spark. 



In Holmes's machine each revolution develops 16 currents in 

 opposite directions ; hence the light produced is not continuous, 

 being extinguished and relighted as many times. As there are 

 500 revolutions per minute, the intervals of darkness are exceed- 

 ingly small. Though unable to demonstrate the intermittence, 

 M. Jamin recognized that the light of the luminous arc was 

 less bright than that from the charcoal points, which he attributes 

 to the interruption of the current. We have, therefore, in this 

 not the discontinuous electric light, but that of the carbon poles 

 heated to intense whiteness, and giving a nearl}^ uniform light. 

 The light of this machine is less blue and poorer in chemical rays 

 than that from a lamp excited by a battery, and therefore better 

 adapted for light-houses. 



The dioptric system of Fresnel as applied to the lanterns of 

 light-houses has been recently described by Mr. Chance before the 

 English Institution of Civil Engineers. It consists of a structure 

 of segments of glass enveloping a central flame, whose focal 

 rays are parallelized in a horizontal direction and deflected in the 



