12—14, and it may also be regarded as tolerably certain that when the earth is in this position in the year 1899 the shoal of little bodies will be in our vicinity. We believe that the earth will actually pass through the shoal, in which case a great meteoric display will be the result—if the weather permits! It may, however, happen that we shall only traverse a sparsely occupied portion of the great host, in which case the shower will fall much short of others which have been recorded. An enormous volume of quite unattainable knowledge would have to be at our disposal were we to be able to predict with certainty all the circumstances of such phenomena; we should have, to know exactly what meteors there were in the shoal, and the dimensions and other features of the orbit which every single meteoroid followed. If such knowledge as this were possible, then the future circumstances of the shower might be predicted with almost as much accuracy as the announcement of the next eclipse or the next opposition of Mars.
This illustration will suffice to explain the reasons why our knowledge of meteorological phenomena is at present in such an imperfect state as compared with those of astronomy. The supreme test of the completeness of any physical theory is the successful prediction of results— we are not yet able to predict great heat-waves or great storms with any assured confidence, not because such phenomena do not observe definite physical laws, but because the knowledge that we should require before we could exactly specify these laws is in a great measure wanting. We are, however, not without grounds for encouragement in the belief that the time may yet come when the definite prediction of meteorological phenomena
