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act with certainty on the prepared paper ; while those which 

 are known to act well, as the oxyhydrogen lime light, are 

 expensive, and difficult to manage. A considerable time 

 since, the author discovered that the light emitted by incan- 

 descent coke, at the " Twyer" (or aperture by which the 

 blast is admitted) of a cupola or furnace for melting cast iron, 

 contained the chemical rays in abundance ; and on lately 

 trying the effect of this light on the prepared paper, he 

 found it was intensely blackened in about forty-five seconds. 

 In the single experiment made, the heat, which was conside- 

 rable, was not separated from the light; but the author pur- 

 posed to make further experiments, in which this precaution 

 will be attended to. 



There is no difficulty to be apprehended in contriving an 

 apparatus to burn a small quantity of coke at a high tempe- 

 rature. A diagram of an apparatus for this purpose was 

 shown. It consists of a vertical tube, nine inches in diameter, 

 lined with refractory clay, and closed at top and bottom. 

 There is a grating about one foot from the bottom, a little 

 above which are two opposite holes, into one of which an air 

 blast from a revolving fanner is projected through the coke, 

 with which the whole tube is filled. The flame passes out 

 at the opposite hole, through a tube so contrived, as to heat 

 the blast of air to a temperature of 500°, just before it enters 

 the coke fire. 



The light from the former lateral aperture is that pro- 

 posed to be used, and issues through a plate of mica or 

 glass opposite to it. This aperture forms part of the con- 

 ductory tube for the blast, which (by passing into the coke 

 in a direction opposite to that in which the light is emitted) 

 keeps the illuminating surface of coke clear from ashes; 

 these are received below the grating, and by a diversion of 

 part of the blast, are blown into the chimney which receives 

 the other products of the combustion. 



As the vertical tube is close above, the combustion can- 



2c 



