For some time I toiled with the others. I saw Nordenholt’s figure close at hand. Then the sky seemed to take on a tinge of violet which deepened suddenly. I saw a black spot before my eyes; and apparently I fainted from loss of blood. * * * * * Even now, the causes of the Chemistry Department disaster are unknown. Henley-Davenport and his two assistants perished instantaneously in the explosion--in fact Henley-Davenport’s body was never recovered from the wreckage at all. A third assistant, who had been in the next room at the time, lived long enough to tell us the exact stage at which the catastrophe occurred; but even he could throw no direct light upon its origin. From Henley-Davenport’s notes, which we found in his house, it seems clear that his efforts had been directed towards producing the disintegration of iron; and that on the morning of the accident he had completed his chain of radioactive materials which furnished the accelerated evolution of energy required to break up the iron atoms. As we know now, he succeeded in his experiment and his iron yielded the short-period isotopes of chromium, titanium and calcium until the end-product of the series--argon--was produced. The four successive alpha-ray changes, following each other at intervals of a few seconds, liberated a tremendous store of intra-atomic energy; but, knowing the extremely minute quantities with which Henley-Davenport worked, it seems difficult to believe that the explosion which destroyed his laboratory was produced by this trace of material. To me it seems much more probable that his apparatus was shattered at the moment of the first disintegration of iron and that thus some of the short-period products were scattered abroad throughout the room, setting up radioactive change in certain of the metallic objects which they touched. No other explanation appears to fit the facts. We shall never learn the truth of the matter now; but knowing Henley-Davenport’s care and foresight, I cannot see any other way of accounting for the violence of the explosion. Luckily for us, no radioactive gas is produced by the disintegration of iron; for had there been any such material among the decay products it is probable that most of those who had run to the scene of the disaster would have perished. * * * * * When I recovered consciousness again I found myself lying on a couch. A doctor was bandaging my hand. Nordenholt, looking very white and shaken, was sitting in a chair by the fire. At first I was too weak to do more than look round me; but after a few minutes I felt better and was able to speak to Nordenholt. “What has happened? Did they get Henley-Davenport out of the wreck?”