THE SMALLEST PARTICLES OF MATTER 29 



Krakatoa, "was observed not fewer than seven times at many of 

 the stations, four passages having been those on the wave travelling 

 from Krakatoa and three those of the wave travelling from its 

 antipodes, after which its traces were lost" (Sir R. Strachy). 



The comparatively recent eruption of Mont Pele, Martinique, 

 was much milder and more akin to the "atomic bomb." On 

 April 25th, 1902, there was a discharge of ashes, and a heavy 

 flow of lava occurred on May 2nd and 3rd. On May 8th a sudden 

 explosion tore away the whole side of the mountain — the gash 

 was clearly visible in 1939 — and released what Zsigmondy called 

 a nuee ardente — a cloud of superheated steam, gases, and col- 

 loidally dispersed particles of rock. About 40,000 persons perished, 

 and all ships in the harbor, except the Roddam, were destroyed. 

 Metal work on the Rodda?n was melted by the blast; but a pris- 

 oner in a dungeon cell in the town was later found alive, though 

 spoons and glass goblets in the room above his cell had been 

 melted. This bespeaks the intense but short-lived heat. It is 

 known that under heat and pressure water "dissolves" in silicates, 

 and the effects may have been due to the sudden explosive release 

 of such a superheated mass, with atomization of the hot rock. 



Dr. Leason H. Adams 24 has advanced the view that volcanism is 

 based on radioactivity, and I give below a note of his theory which he 

 kindly prepared at my request: 



"The central problem of volcanism is to devise a mechanism which 

 will explain the existence of local hot spots in the Earth's crust, 25 

 whereby at present, as during past geological epochs, eruptions of 

 molten lava and hot gases may take place in localized areas. Volcanism 

 is still a highly controversial subject among geologists and geophysi- 

 cists, though many attempts have been made to explain it. A theory 

 which has appealed to some of those who have given much attention 

 to the subject attributes the local heating to slight variations in the 

 average radioactive content of the rocks forming the crust in the active 

 area. The theory is based on the following considerations: 



"(1) The rocks of the Earth's crust contain a minute but very 

 important amount of uranium and its disintegration products, includ- 

 ing radium. In terms of radium, the amount of radioactive material 

 in the usual igneous rocks is of the order of magnitude of one part in 

 a million million; but the heat generated by even this minute amount 

 of radium in a volume of rock measured in cubic miles, is very con- 

 siderable. 



"(2) The temperature gradient in the crust of the Earth (now judged 

 to be more than 2,000,000,000 years old) is profoundly affected by 



