[bronson] the HALIFAX EXPLOSION 35 



not over an eighth of an inch. It seems probable that this must 

 have been due to a failure to record. 



There is another type of phenomenon, quite common within half 

 a mile of the explosion, which deserves especial notice. The fact is 

 thoroughly well-established that persons and many heavy objects 

 were picked up from the ground and carried considerable distances. 

 In one case a man was taken from the roof of a high building, about 

 three-quarters of a mile from the explosion, and gently deposited on 

 the ground. One of the best examples of this type of phenomenon 

 occurred on the ship Picton, which was at its wharf about 250 meters 

 from the explosion. A great boulder, weighing more than a ton, was 

 picked up from somewhere and dropped on the ship. It crashed 

 through the upper deck and still lies on the deck below. The surface 

 of the boulder is worn smooth, suggesting that it must have come from 

 the beach or the harbour bottom, but it was certainly not washed on 

 board for no water came over the vessel. Such phenomena show 

 that the air disturbance was something more than an intense com- 

 pressional wave travelling out in a straight line. There must also 

 have been some kind of vortex motion, such as occurs in cyclones. 



The seismograph record of the explosion obtained at Dal- 

 housie University is of more than passing interest, because three 

 distinct shocks are recorded. The first occurred at about 9:05, the 

 second five minutes later, and the third an hour after the first. The 

 explosion was almost directly north of the instrument and unfortu- 

 nately the N.-S. pendulum caught at the extremity of the first swing, 

 which made it impossible to attempt any energy calculations from it. 

 The E.-W. record is not purely seismic but exhibits oscillations of the 

 pendulum. The three records on this component have much the 

 same character and are of practically the same magnitude. The 

 natural conclusion is that there must have been three explosions, 

 though the two later ones were neither seen nor felt by the public. 

 The only explanation so far suggested is that the entire mass of 

 explosive was not detonated at first and that small quantities exploded 

 later on the bottom of the harbour. In this case it must have been 

 so confined as not to produce any air concussion and the slight motion 

 of the earth might have escaped notice. This explanation has many 

 serious objections and Mr. Cope considers it untenable. 



The writer regrets the fragmentary nature of the data contained 

 in this paper and hopes that it may be possible to supplement at it 

 at some future time. 



