Supposing, for instance, that, by some malevolent agency, all the tunnels in this country were put out of action, what sort of plight should we be in? To take the most obvious thing first, long-distance traffie on the main line railways would come to a standstill because the railway systems would be, for the most part, cut up into short, isolated lengths; and a11 London's tube services wouId cease to run. That would be bad enough for those of us who have much travelling to do. But far more serious would be the interruption of supplies -food, coal, munitions, and many other things that are more than ever vital to us nowadays. That, however, is by no means the complete picture. You who live in several of our larger towns and cities would lose most, if not all, of your water supplies, because they are brought to you from distant reservoirs by aqueducts which, in parts of their lengths are tunnels. (Big tunnels they are, too; a lorry could be driven through some of them if they were empty of water.) Another calamity would be the stopping up of sewage systems in scores of towns up and down the country; in most large centres of population parts, at least, of these systems will have been constructed by tunnelling. (I wonder if Londoners realize that there are upwards of 400 miles of

88 SCIENCE AT YOUR SERVICE main sewers alone in the vast drainage network of their city.) Again, there would be failure of eleetric supplies from those great power stations-and there are quite a few-in which the condensing water essential to the operation of modem turbine plant is circulated through tunnels.