COLLISION OF STEEL WITH HARD BODIES. 105 



the metal is not fufficient to raife the temperature of fteel wire, 



or a fteel plate, fo as to caufe it to enter into the vivid combuf- 



tion, yet in a&ing upon fuch a minute filament as that {truck 



off in the gunlock, it may be fufficient to keep up the procefs in cafe thcfur- 



of oxidation till it becomes fo vivid as to occafion the ftrongeft g^at ii^prepor- 



heat and light. Befides, the furface of this filament is very tion to the mafs. 



great as compared with its bulk, and the oxide produced upon 



it is lefs likely to form a coat which might defend the interior 



parts from the action of the air *. 



It would not be difficult to find many analogous inftances, Other inftances. 

 in which the progrefs of oxidation is dependent upon the mafs^. ]n ° c {JjJjjJ J°* 

 of the combuftible body, or rather upon the relation of this fire in fmall 

 mafs to furface; thus, a very thin and fmall bit of phofphorus ma(res * 

 will inflame fpontaneouily, and burn with the vivid light when 

 wrapped up in filaments of fine cotton ; whilft a thicker and 

 larger piece will only fhine with the feeble blue light : and 

 though a large mafs of zinc may be melted in the atmofphere 

 without inflaming, a fmall and thin (having will burn vividly 

 long before it is heated to the temperature of fufion. 



V. In confidering the general phenomena of the production Not probable 

 of heat and light, by mechanical means, it is difficult to con- i^ould be pro^ 

 ceive that any confiderable increafe of temperature can be pro- duced by a fmglo 

 duced on a metallic furface by a {ingle collifion ; for the. con- collli " lon * 

 dueling power of the metals is fuch as would fpeedily caufe 

 the heat to be communicated to the contiguous parts ; and 

 even in the cafe of the abrafion of minute particles, though 

 the time required for their feparation from the mafs is to us 

 imperceptible, yet it rauft be fufficient to enable them to give 

 out to it a portion of their heat. 



The bodies that become luminous by being (truck or rubbed Luminous ap- 

 together, in vacuo, or in gafes that do not contain oxigen, r |2gJJ2 W 

 under water, fuch as fluate and carbonate of lime, filiceous phofphoref- 

 flones, glafs, fugar, and many of the compound falts, are c . ence » ty fat* 

 both electrics per ft, and phofphorefcent fubflances ; fo that 

 the flalhes they produce are moft likely occafioned, partly by 



* In turning very fine work of fteel in the lathe, fo as to afford 

 {havings or threads much thinner than one-thoufandth of an inch, 

 I found that this metallic wool very readily caught fire at a candle, 

 and burned throughout in quantities of a cubic inch or more : But 

 it was fcarcely fo much oxided as to haye loft its flexibility after this 

 sombuftion.— N, 



the 



