122 SECTIONAL ADDRESSES. 



example of the carrying away of years of work at Antofagasta Harbour, 

 Chile, by a series of tidal waves. Yet there is no existing formula extant 

 which would have enabled the civil engineer to forecast this appalling 

 disaster. The influence of sea action on structures built up of units of 

 mass and at varying depths of water is not at the moment governed by 

 precise knowledge, and the forms of breakwaters vary the world over. 

 There ought surely to be some means of collating data for the guidance of 

 civil engineers in the design of marine works, which would save them from 

 having to rely alone on the failures or successes of those who have gone 

 before. 



Voids. 



The influence of air and water-filled voids and the effect they have on 

 many matters that affect engineering practice is not, I think, fully realised. 



Their bearing and their influence on design include within their range 

 such widely different subjects as the solidity of breakwaters, their cost 

 and their resistance to sea action ; the combustion of fuels, both solid 

 and liquid, and especially their rapidity of burning, ranging from explosions, 

 in the case of propellants and blasting powders, to the corrosion of metals 

 by oxidation. The minuteness of particles and the voids which surround 

 them turn some innocent substances, such as coal-dust and flour-mill-dust, 

 into dangerous explosives, and this is due to the intimate association of 

 the air and its contained oxygen with the minute sub-division of their 

 ' mass when they are powdered by grinding. The economy of fuel, both 

 liquid and solid, when burning, is greatly enhanced by its fine sub-division, 

 especially if provision for its intimate association with the atmosphere is 

 arranged for. Explosion, as compared with combustion, is only a question 

 of rapidity of combustion, the other extreme being the slow deterioration 

 of metals due to oxidation as exemplified in the rusting of steel and iron 

 structures. These examples show what a wide range there is in the 

 phenomena that are in some measure attributable to the voids surrounding 

 the particles of materials and their more or less intimate association with 

 air. 



I propose to give some examples later which have occurred in my own 

 experience, and which emphasise the question of the importance played 

 by voids in engineering work. 



Another aspect of this subject is exemplified in capillary attraction, 

 or the capacity of certain mixtures of minute particles either in a loose 

 form or in the form of porous solids, which have the power of defjdng the 

 action of gravity by raising water. In some cases I have known water 

 raised several feet, which seems to me to indicate the existence of a power 

 that so far does not seem to me to have been adequately defined and has 

 some analogy, I imagine, to the diffusion of gases. This power, possessed 

 by some materials, which do not dissolve in water, of acting in an un- 

 expected way on contained fluids, when such fluids are free to move by 

 gravity to lower levels, is due to something not to my knowledge fully 

 explained. I imagine capillary attraction may be analogous to the flow 

 of sap in growing vegetation. It might be due, though I have never heard 

 it suggested, to changes of temperature that might produce this movement 

 of vegetable fluids contrary to gravity. It is certainly not so in very fine 



