178 THE PRINCIPLES OF SCIENCE. 



cerning the relative approach or recession of many stars 

 as regards the earth. 



Tides are vast waves, and were the earth's surface 

 entirely covered by an ocean of uniform depth, they would 

 admit of very exact theoretical investigation. The wholly 

 irregular form of the several seas introduces unknown 

 quantities and complexities with which theory cannot cope. 

 Nevertheless, Whewell, observing that the tides of the 

 German Ocean consist of interfering waves, which arrive 

 partly round the north of Scotland and partly through 

 the British Channel, was enabled to predict that at a point 

 about midway between Lowestoft and Brill on the coast 

 of Holland, in latitude 52 27' N, and longitude 3 h. 

 1 4m. E, no tides would be found to exist. At that point 

 the two waves would be of exactly the same amount, but 

 in opposite phases, so as to neutralise each other. This 

 assertion was verified by a surveying vessel of the British 

 navy - v . 



Prediction in other Sciences. 



Generations, or even centuries, will probably elapse 

 before mankind are in possession of a mathematical theory 

 of the constitution of matter as complete and satisfactory 

 as the theory of gravitation. Nevertheless, mathema- 

 tical physicists have in recent years acquired a fair hold 

 of some of the simple relations of the physical forces to 

 matter, and the proof is found in some remarkable anti- 

 cipations of curious phenomena which had never been 

 observed. Professor James Thomson deduced from Car- 

 not's theory of heat that the application of pressure would 

 lower the melting-point of ice. He even ventured to 

 assign the amount of this effect, and his statement was 



v Whewell's 'History of the Inductive Sciences,' vol. ii. p. 471. 

 Herschel's 'Physical Geography,' 77. 



