WHAT THIS WORLD IS MADE OF 



thin that they were transparent, and shone with 

 a pale green. Heated a little, they lost all color 

 and became entirely transparent. The light came 

 through this gold as it does common glass. Yet so 

 far as the microscope could reveal, it was perfectly 

 continuous ; there were no holes in it. This is prob- 

 ably the thinnest solid metal possible to produce. 

 Nevertheless, by dissolving gold and then deposit- 

 ing it in a thin layer on glass, Faraday was able to 

 go ten times further. Such layers, he says, were 

 probably not continuous, "yet they acted like 

 plates towards the light." According to his esti- 

 mate, there would be five hundred or a thousand 

 such layers to a wave-length. Thus they would 

 have been only from one to one-half a micro-mi- 

 cron thick (i nfi to 0.5 fifi). 



If Faraday was right, then with his chemically 

 treated gold-leaf he surpassed what was long sup- 

 posed to be the thinnest continuous substance 

 known. This was the wall of a soap - bubble. 

 People who left off blowing soap-bubbles with 

 their childhood may be interested to know that 

 these childish playthings have engaged some of the 

 greatest of scientific minds. Newton was one. 

 Everybody has observed that, just as the soap- 

 bubble is about to break, little black spots ap- 

 pear, and if the bursting of the bubble were not 

 so quickly done we should see that it is at these 



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