34 THE ROYAL SOCIETY OF CANADA 



It is interesting to notice how closely the experience of this 

 explosion, as regards the distance at which damage was done, fits in 

 with the results of past explosions, and with experiments. If d is the 

 maximum distance in meters from the explosion to points at which 

 definite damage is done, and m is the mass of explosive in kilograms, 

 then the expression d = K-v/m has been found to agree pretty welli 

 with the observed facts. K is a constant which depends on the 

 nature of the explosive and is about 10 in the case of high explosives. 

 Applying this formula to the Halifax explosion, where m = 2,370,000 

 kg., d came out to be 15,400 meters. This distance is in satisfactory 

 agreement with such information as I have thus far gathered regarding 

 the maximum distances at which real damage was done. 



It seems to be the generally accepted opinion that the intense 

 compressional wave is followed by a wave of rarefaction of much less 

 intensity. Whether this is the true explanation of the phenomena 

 or not, it is certainly true that windows, doors and walls sometimes 

 fell in toward the explosion though much more frequently away from 

 it. One of the most interesting illustrations of this was seen about 

 half a mile from the explosion on the Dartmouth side of the harbour. 

 At a point nearly opposite the point of explosion, the highway was 

 lined by a row of fir trees from six to twelve inches in diameter. These 

 were uprooted and pointed away from the explosion centre where 

 there was no obstruction between them and the explosion, but along 

 that part of the road where there is a forest of these trees between the 

 road and the harbour, the uprooted trees fell towards the explosion. 



Further confirmation on this point, and other interesting infor- 

 mation, was obtained from several barograph records, two of which 

 the writer has in his possession. Both instruments were located near 

 the centre of the city, about 3,000 meters from the explosion. The 

 motion of the pens was so rapid and so great that there is uncertainty 

 regarding the magnitude of the motion, and it seems quite possible 

 that both pens went off the paper entirely. However, it can be safely 

 said that the positive motion was much greater than the negative. 

 The record from the Halifax Club shows at least a motion of + 1-25 

 in. and — -45 in. and the one from the Halifax Nautical Instrument 

 Co. shows at least + -75 in. and — -45 in. There were at least two 

 other barograph records obtained in the city; one at the Dockyard 

 within 300 meters of the explosion and the other on the cable ship 

 Mmia, about 3,000 meters from the explosion. The needle of the 

 latter instrument went completely off the paper and did not return 

 to its previous position. The record at the Dockyard has been lost, 

 but the observer reports that the change in pressure was very small, 



