6j2 PHILOSOPHICAL TRANSACTIONS. [ANNO 1785. 



ceding may be observed in a common kitchen fire. When it is faintest, its 

 colour is most red, the other rays having been emitted, and the combustion at a 

 stand ; but by blowing on it in this state, its brightness will be increased, and 

 more and more of the rays which are yielded by the internal parts of the body 

 will come to the eye, till at length, by continuing to blow, the combustion will 

 be made so complete as to yield all the rays, or to make it appear perfectly 

 white 



Many are the varieties discoverable in the flames and in the appearances of 

 fixed burning bodies, to which the preceding observations may be applied ; but, 

 to avoid unnecessary amplification, I will take notice only of what appears to me 

 an imperfection in Sir Isaac Newton's definition of flame. He conjectures, that 

 it may be a vapour heated red-hot. I think I should rather say, that flame is an 

 instance of combustion whose colour will be determined by the degree of de- 

 composition which takes place. If it be very imperfect, the most refrangible 

 rays only will appear. If it be very perfect, all the rays will appear, and its 

 flame will be brilliant in proportion to this perfection. There are flames how- 

 ever which consist of burning particles, whose rays have partly escaped before 

 they ascended in the form of vapour. Such would be the flame of a red-hot 

 coal, if exposed to such a heat as would gradually disperse it into vapour. When 

 the fire is very low under the furnace of an iron foundry, at the upper orifice of 

 the chimney a red flame of this kind may be seen, which is different from the 

 flame that appears immediately after fresh coals have been thrown on the fire ; 

 for, in consequence of adding such a supply to the burning fuel, a vast column 

 of smoke ascends, and forms a medium so thick as to absorb most of the rays 

 excepting the red. 



Experiments on electric light. — If we wish to procure any degree of certainty 

 in any hypothesis which we may form concerning electrical light, perhaps the 

 following general deductions may be of some service to us. 1. There is no fluid 

 or solid body in passing through which the electric fluid may not be made lumi- 

 nous. In water, spirits, oil, animal fluids of all kinds, the discharge of a 

 Leyden phial of almost any size will appear very splendid, provided we take care 

 to place them in the circuit, so that the fluid may not pass through too great a 

 quantity ol them. My general method is to place the fluid, on which I mean 

 to make the experiment, in a tube -f- of an inch in diameter, and 4 inches long. 

 I stop up the orifices of the tube with 2 corks, through which I push two 

 pointed wires, so that the points may approach within J- of an inch to each 

 other. The fluid in passing through the interval between the wires is always 

 luminous, if a force be used sufficiently strong. The glass tube, if not very 

 thick, always breaks when this experiment succeeds. To make the passage of 

 the fluid luminous in the acids, they must be placed in capillary tubes, and two 



