170 



valuable; and, with some contrivance for heating the blast, its uses 

 may possibly be greatly extended in the manufacture of things made of 

 iron, or of things made of other metals in contact with iron. 



But these industrial considerations are out of place here, my object 

 being to deduce scientific considerations from material facts, connected 

 with mechanical art, which I have ventured to speculate on, with the 

 view, if possible, of tracing the original development of a scientific prin- 

 ciple, which, though hitherto appHed in the arts only, may possibly be 

 turned to account as a means by vv^hich we may obtain any amount of 

 iron light, or light produced by the combustion of iron, ]per se, that we 

 may want for scientific purposes. 



Iron burned by the horse-shoe nail-maker's process, carried one step 

 further, may be considered to be an aerolith at rest, — the air from the 

 cylindrical bellows moving past it with the same velocity with which 

 an aerolith in motion would, under ordinary circumstances, travel through 

 the lower region of the atmosphere, and there, by friction, first become 

 hot, and next, by impact with oxygen,*^' begin to burn its iron and nickel, 

 like the heated nail-rod when exposed to the cold blast. 



The partial combustion of the iron in the nailer's process, though it 

 in theory, in some respects, resembles that produced by the burning of 

 iron in oxygen gas, differs from it materially, and also from Bessemer's 

 process, in the prod action of no large explosive sparks, which divert our 

 attention from the iron actually burning. In our process the sparks 

 are very minute, and the burning iron gives a very strong light, its in- 

 tensity appearing to depend on the violence of the blast. We are thus 

 supplied with a means of producing a large quantity of steady light 

 by the combustion of iron for optical experiments. And as iron-wire 

 may be mixed with other wire, and simple or compound wicks pro- 

 duced, made out of twisted hanks of wire of one or more kinds of metal, 

 we have at our command a ready method for producing lights, which 

 may be compared with light produced by the sun or meteoric bodies, in 

 which there is reason to suspect the combustion of iron and other me- 

 tallic substances. 



So far as the material facts noticed in this paper are concerned, there 

 is nothing actually new in it ; yet I cannot find that any one has drawn 

 the attention of opticians and physicists to the nailer's process of par- 

 tially burning iron, or its analogies with the other processes noticed, 

 and the means it pats at our command of burning iron by itself as a 

 source of light. 



Not having tried any experiments on the light produced by the 

 nailer's process of burning iron, I am not prepared to say whether it 

 ofi'ers any promise to the photographer ; but, as highly heated iron is 



* The spark produced by a flint and steel is an example of the combustion of iron, first 

 heated by pressure, and afterwards burnt by motion through the air. Its colour is dif- 

 ferent to that of iron burnt by the nailer's process, though the colour of that may change 

 with the increase of the blast, and the proportional intensity of the light. 



