124 SECTIONAL ADDRESSES. 



results. It is, for example, much more difficult to make water-tight 

 masonry than water-tight concrete, because it is more difl&cult to 

 thoroughly fill the voids in the masonry joints with a trowel or by bedding 

 the stones in mortar than by mixing the ingredients as in concrete. 



Further, in earthen dams and in earthen railway embankments the 

 question of settlement is very largely bound up with the amount of voids 

 left in the material when it is tipped. 



During my work in the United States for the British Government 

 during the war — -1915-16 — I had an interesting experience arising out of 

 the testing of time fuses and the effects of voids thereon. The firm which 

 had made many thousands of this particular fuse — it was called a No. 185 

 time fuse — had been very accurate in their manufacture up to a point ; 

 the timing had been very regular and the percentages of error on proving 

 at the range very small. Suddenly, however, the proving guns told 

 another story, and the timing of the bursting of the shrapnel was distinctly 

 bad. I visited the factory where these fuses were made and went minutely 

 into the possible causes of the change, xls to the chemical analysis of 

 the powder, which was compressed into the time-burning rings, there 

 was no change indicated in this analysis and no change in manufacture 

 or in the pressing of it into the time ring. For a time we were all at a 

 loss to account for what was happening. I remembered, however, that 

 British Navy cordite made in England had holes cast through the blocks 

 which go to form propellants for big gun charges. These were carefully 

 proportioned to admit of association of the air surrounding such cast 

 blocks (by perforation) in order to regulate the speed of combustion. I 

 thought there must be something, therefore, changed in the volume of 

 the voids and of the contained air arising out of the handling of the powder 

 when in transit to the factory. I asked the head of the firm whether he 

 had recently changed the method of transport. He said, ' Yes, we have. 

 We have been making an addition to our factory, and while this has been 

 going on we have had to bring the powder in by motor lorries over 

 temporary roads instead of by railway wagon.' ' Well,' I said, ' I think 

 this is the secret of the errors in the timing of the fuses you have made, 

 for the powder has evidently been brought in over the rough roads made 

 of tree trunks (called " corduroy " roads in America), and has been more 

 shaken than it had been when delivered by rail ; the voids between the 

 particles have been made less in consequence, and the included air is 

 therefore less in amount, and contact with the particles of powder and 

 the rate of burning is consequently different. This, then, is the possible 

 cause of the burning in the time rings being irregular.' 



To make a long story short, this was investigated and found to be the 

 case, and when this rough motor transport was eliminated the same 

 powder performed its proper function just as exactly as it had done before 

 this temporary method of transport was introduced and without any 

 change in composition or treatment in the manufacture of the fuses. 



The breakwater I have just been constructing in Valparaiso Harbour, 

 Chile, is founded in 187 feet of water upon a sandbank. This bank is 

 deposited by suction dredgers from neighbouring foreshores within 

 ten miles. It has spread out at its base to over a quarter of a mile in 

 width, and the sand, in its passing through this great depth of water, has 



