Prop. W. M. Thornton on Thunderbolts. 633 



should both be negatively charged at the same instant. It 

 would be the normal thing for the ball to approach the earth 

 with considerable velocity, as is recorded in well authenticated 

 cases. The fact that sometimes it turns off parallel to the 

 earth's surface indicates that if, at the moment of the 

 last discharge, the earth was locally positive, its sign has 

 changed by reason of the electrical discharge, and is as usual 

 negative. 



The reason why the gas gathers into a sphere is that since 

 the energy of ozone is for a given mass greater than that of 

 oxygen, whilst the volume is less, the force between molecules 

 of oxygen and ozone is an attraction, which decreases in the 

 aggregate as recombination proceeds until it has the same 

 value as the repulsion due to the usual molecular bombardment 

 in gases. The temperature rising on account of the heat 

 set free equilibrium would be quickly reached, the cooling 

 of the ball by radiation and its motion through the air giving 

 it stability. On reaching water, for which ozone has a strong 

 affinity, or anything which causes ozone to decompose with 

 great rapidity ^ the ball explodes. 



The most conclusive evidence for any suggested constituent 

 is whether this contains energy in such a form that it can be 

 quickly liberated. It is well known that ozone reverts to 

 oxygen, and it remains to see whether the energy liberated 

 by this change is sufficient to account for the effects observed 

 on its sudden occurrence. 



In the conversion of a gramme of oxygen into ozone 

 29*6 kilogramme-degree-centigrade units of heat are ab- 

 sorbed. A sphere of 50 cm. diameter contains 62*5 litres. 

 For the complete change of oxygen at 1*45 grammes per litre 

 to this volume of ozone at 2*14 grammes per litre, there would 

 be required 2615 of the above heat units. A clearer view of 

 what this means is obtained hy expressing it in mechanical 

 units. Each kilogramme-degree unit is equivalent to 3094 

 foot-pounds ; the total energy of transition is therefore 

 8 million foot-pounds. 



It is unlikely, since there is recombination proceeding by 

 diffusion within the ball as it falls, that the whole mass could 

 be pure ozone on reaching the earth, but the dissipation of 

 one tenth of the above energy explosively in the tenth of a 

 second is at the rate of 15,000 horse-power. 



The energy of the explosion-wave is well accounted for by 

 this. There is in addition the sudden expansion when ozone 

 is changed into oxygen, in this case 20 litres for a sphere of 

 50 cm. diameter of ozone. 



Phil. Mag. S. 6. Vol. 21. No. 125. May 1911. 2 T 



