"The hollow masts of our ships--to glance at another phase en passant--carry windmills instead of sails, through which the wind performs the work, of storing a great part of the energy required to run them at sea, while they are discharging or loading cargo in port; and it can, of course, work to better advantage while they are stationary than when they are running before it. These turbines are made entirely of light metal, and fold when not in use, so that only the frames are visible. Sometimes these also fold and are housed, or wholly disappear within the mast. Steam-boilers are also placed at the foci of huge concave mirrors, often a hundred feet in diameter, the required heat being supplied by the sun, without smoke, instead of by bulky and dirty coal. This discovery gave commercial value to Sahara and other tropical deserts, which are now desirable for mill-sites and for generating power, on account of the directness with which they receive the sun's rays and their freedom from clouds. Mile after mile Africa has been won for the uses of civilization, till great stretches that were considered impassible are as productive as gardens. Our condensers, which compress, cool, and rarefy air, enabling travellers to obtain water and even ice from the atmosphere, are great aids in desert exploration, removing absolutely the principal distress of the ancient caravan. The erstwhile 'Dark Continent' has a larger white population now than North America had a hundred years ago, and has this advantage for the future, that it contains 11,600,000 square miles, while North America has less than 9,000,000. Every part of the globe will soon sustain about as large and prosperous a population as the amount of energy it receives from the sun and other sources will warrant; public debts and the efficiency of the governments being the variable elements.
"The rabbits in Australia, and the far more objectionable poisonous snakes in South America and India, have been exterminated by the capture of a few dozen of the creatures in the infested districts, their inoculation with the virus similar to the murus tiphi, tuberculosis or any other contagious-germ complaint to which the species treated was particularly susceptible, and the release of these individuals when the disease was seen to be taking hold. The rabbits and serpents released at once returned to their old haunts, carrying the plague far and wide. The unfortunate rabbits were greatly commiserated even by the medicos that wielded the death-dealing syringe; but, fortunately for themselves, they died easily. The reptiles, perhaps on account of the wider distribution of the nerve centres, had more lingering but not painful deaths, often, while in articulo mortis, leaving the holes with which they seemed to connect their discomfort, and making a final struggle along the ground, only to die more quickly as a result of their exertions. We have applied this also to the potato-bug, locust, and other insect pests, no victim being too small for the ubiquitous, subtle germ, which, properly cultivated and utilized, has become one of man's best friends.
"We have microbe tests that show us as unmistakably whether the germs of any particular disease--like malaria, typhoid, or scarlet fever--are present in the air, as litmus-paper shows alkalinity of a solution. We also inoculate as a preventive against these and almost all other germ diseases, with the same success that we vaccinate for smallpox.
"The medicinal properties of all articles of food are so well understood also, that most cures are brought about simply by dieting. This, reminds me of the mistakes perpetrated on a friend of mine who called in Dr. Grave-Powders, one of the old-school physicians, to be treated for insomnia and dyspepsia. This old numskull restricted his diet, gave him huge doses of medicine, and decided most learnedly that he was daily growing worse. Concluding that he had but a short time to live, my friend threw away the nauseating medicines, ate whatever he had a natural desire for, and was soon as well as ever--the obvious moral of which is, that we can get whatever treatment we need most beneficially from our food. Our physicians are most serious and thoughtful men. They never claim to be infallible, but study scientifically to increase their knowledge and improve the methods of treatment. As a result of this, fresh air, regular exercise for both sexes, with better conditions, and the preservation of the lives of children that formerly died by thousands from preventable causes, the physique, especially of women, is wonderfully improved, and the average longevity is already over sixty.
"Our social structure, to be brief, is based on science, or the conservation of energy, as the Greek philosophers predicted. It was known to them that a certain amount of power would produce only a certain amount of work--that is, the weight of a clock in descending or a spring in uncoiling returns theoretically the amount of work expended in raising or coiling it, and in no possible way can it do more. In practice, on account of friction, etc., we know it does less. This law, being invariable, of course limits us, as it did Archimedes and Pythagoras; we have simply utilized sources of power that their clumsy workmen allowed to escape. Of the four principal sources--food, fuel, wind, and tide--including harnessed waterfalls, the last two do by far the most work. Much of the electrical energy in every thunderstorm is also captured and condensed in our capacious storage batteries, as natural hygeia in the form of rain was and is still caught in our country cisterns. Every exposed place is crowned by a cluster of huge windmills that lift water to some pond or reservoir placed as high as possible. Every stiff breeze, therefore, raises millions of tons of water which operate hydraulic turbines as required. Incidentally these storage reservoirs, by increasing the surface exposed to evaporation and the consequent rainfall, have a very beneficial effect on the dry regions in the interior of the continent, and in some cases have almost superseded irrigation. The windmill and dynamo thus utilize bleak mountain-tops that, till their discovery, seemed to be but indifferent successes in Dame Nature's domain. The electricity generated by these, in connection with that obtained by waterfalls, tidal dynamos, thunderstorms, chemical action, and slow-moving quadruple-expansion steam engines, provides the power required to run our electric ships and water-spiders, railways, and stationary and portable motors, for heating the cables laid along the bottom of our canals to prevent their freezing in winter, and for almost every conceivable purpose. Sometimes a man has a windmill on his roof for light and heat; then, the harder the wintry blasts may blow the brighter and warmer becomes the house, the current passing through a storage battery to make it more steady. The operation of our ordinary electric railways is very simple: the current is taken from an overhead, side, or underneath wire, directly through the air, without the intervention of a trolley, and the fast cars, for they are no longer run in trains, make five miles a minute. The entire weight of each car being used for its own traction, it can ascend very steep grades, and can attain high speed or stop very quickly.
"Another form is the magnetic railway, on which the cars are wedge-shaped at both ends, and moved by huge magnets weighing four thousand tons each, placed fifty miles apart. On passing a magnet, the nature of the electricity charging a car is automatically changed from positive to negative, or vice versa, to that of the magnet just passed, so that it repels while the next attracts. The successive magnets are charged oppositely, the sections being divided halfway between by insulators, the nature of the electricity in each section being governed by the charge in the magnet. To prevent one kind of electricity from uniting with and neutralizing that in the next section by passing through the car at the moment of transit, there is a "dead stretch" of fifty yards with rails not charged at all between the sections. This change in the nature of the electricity is repeated automatically every fifty miles, and obviates the necessity of revolving machinery, the rails aiding communication. "Magnetism being practically as instantaneous as gravitation, the only limitations to speed are the electrical pressure at the magnets, the resistance of the air, and the danger of the wheels bursting from centrifugal force. The first can seemingly be increased without limit; the atmospheric resistance is about to be reduced by running the cars hermetically sealed through a partial vacuum in a steel and toughened glass tube; while the third has been removed indefinitely by the use of galvanized aluminum, which bears about the same relation to ordinary