g4 PHILOSOPHICAL TRANSACTIONS. [aNNO 1776. 



be ignited. One of the means of producing heat is inflammation ; and this, as 

 is well known, is suflicient for ignition. But besides the light produced by igni- 

 tion, there is also light produced by the inflammation itself. For the investiga- 

 tion of this principle, it will be necessary to consider ignition in the first place. 



Substances, heated to between 6 and 700° of Fahrenheit's thermometer, 

 begin to be luminous in the dark. If they be colourless, the light which is first 

 observed is red ; as the heat is increased, there is a mixture of yellow rays ; and 

 lastly a due proportion of all the coloured rays to form a pure white, which has 

 been commonly called, by chemists, a melting heat. The intenseness of this 

 light depends much on the density of the heated body ; for while metals, heated 

 to this degree, throw out a strong light, the vapour at the end of the flame of a 

 blow-pipe, properly applied to a lamp, is not visibly luminous, though the heal 

 be so great as immediately to give a white heat to glass. I'he colour of this 

 light is aftected by the colour of the ignited matter. While zinc is calcining, 

 the pure white calx throws off a light, which vies with that of the sun in bright- 

 ness and purity ; the green calx of copper gives to the flame of a fire, in which 

 it is calcining, a beautiful green ; and tallow burning in a candle, being con- 

 verted into empyreumatic oil, as it passes off from the wick, the yellow colour 

 of this oil gives a yellowness to the flame, which very much alters the colours of 

 objects seen by candle liglit from what they appear to be in the day. 



The light produced by the decomposition of bodies in inflammation is totally 

 independent of the heat, and its colour is blue; for substances which burn, 

 without producing 6oo° of heat of Fahrenheit's thermometer, give light during 

 their inflammation. Thus, phosphorus of urine, exposed to the air, burns and 

 is decomposed, producing light with very little heat ; and that this is a true in- 



was admitted a Fellow of the College of Physicians. At this time the college was occupied in re- 

 vising its Pharmacopoeia, a business for which Dr. F. w as peculiarly qualified ; accordingly it is said 

 tliat many of tlie improvements, especially in the chemical processes, were suggested by him. 



Dr. F.'s medical works consist of Elements of tlie Practice of Physick ; a Treatise on the Digestion 

 of the Food ; his 4- Dissertations on Fever ; and 3 Memoirs inserted in the Medical ;md Chinirgical 

 Transactions. His piiilosophical writings, besides his Elements of Agriculture and Vegetation, con- 

 sist of die following papers, many of them relating to chemistry, inserted in tlie Phil. Trans, 

 namely, the present paper on tlie Light produced b)' Inflammation ; an Examination of various 

 Ores in the Museum of Dr. \V. Hunter, (Phil. Trans, vol. 6y ;) A New Method of Assaying Copper 

 Ores, (Ibid. vol. 70 ;) Experiments on tlie Loss of Weight in Bodies when Melted or Heated, (Ibid. 

 vol.71;) Account of an Experiment on Heat, ^Ibid. vol. 77 ;) the Cronian Lecture on Muscular 

 Motion, (Ibid. vol. 7S ;) On the Cause of tlie additional Weight of Metiils on being C;Ueined, (Ibid, 

 vol. 82 ;) Account of a New Pendulum, being tlie Bakerian lecture. Dr. F. was moreover tlie au- 

 tlior of those curious experiments related by Sir Clias. Blagden, (Phil. Trans, vol. 65;) in which 

 different persons were exposed to high degrees of temperature, in rooms heated for the purpose. 



For otlier particidars concerning Dr. F., tlie reader is referred to tlie Gent. Mag. and Month. Mag. 

 (()r the year 18o'2. 



