66 DIVERSIONS OF A NATURALIST 



scrape one with the other very firmly, you will produce 

 a flash of light of an orange or reddish colour. And at 

 the same time you will notice a very pecular smell, 

 rather agreeable than otherwise, like that of burning 

 vegetable matter. It would seem that the rubbing 

 together of the stones produces a fine powder of some of 

 the siliceous substance of the stone and at the same 

 time a very high temperature, which sets the powder 

 aflame. I had the idea at one time, based on the curious 

 smell given out by the flashing pebbles, that perhaps 

 it was a thin coating of vegetable or other organic 

 matter derived from the sea-water which burns when the 

 stones are thus rubbed together; but I found on chemi- 

 cally cleaning my pebbles, first with strong acid and 

 then with alkali, that the flame and the smell were 

 produced just as well by these chemically clean stones 

 as by those taken from the beach. The flame produced 

 by the rubbing of the two stones seemed then to be like 

 the sparks obtained by strike-a-lights of flint and 

 steel, or the prehistoric flint and pyrites. Now, however, 

 a new fact demands consideration. The supposition 

 that the powdered silica formed, when one rubs the two 

 pebbles together, is actually " burnt," that is to say, 

 combined with the oxygen of the air by the great heat 

 of the friction, is rendered unlikely by the fact that if 

 you perform the rubbing operation in a basin of water 

 with the stones submerged, the flash is produced as 

 easily as in the air. My attention was drawn to this 

 fact by a letter from the well-known naturalist the 

 Rev. Reginald Gatty. I at once tried the experiment 

 and found the fact to be as my correspondent stated. 

 Not only so, but the smell was produced as well as the 

 flash. 



With the desire to get further light on the subject, 



