From "Scientific Ideas of To-day." 



DETECTING A SMALL QUANTITY OF MATTER 



In the left-hand photograph the two pieces of paper exactly balance. The balance used is very sensitive, and when the single word 

 "atoms" has been written with a lead pencil upon one of the papers the additional weight is sufficient to depress one of the pans 

 as shown in the second photograph. The spectroscope will detect less than one-millionth of the matter contained in the word p^^riH^d 

 above. 



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Photo: National Physical Laboratory. 

 AN X-RAY PHOTOGRAPH OF A GOLF BALL, 

 REVEALING AN IMPERFECT CORK 



Reproduced by permission of X-Rays Lid. 



THIS X-RAY PHOTOGRAPH IS THAT OF A HAND OF A 

 SOLDIER WOUNDED IN THE GREAT WAR 



Note the pieces of shrapnel which are revealed. 



