CONTRIBUTIONS TO SCIENCE. 513 



the ring in the direction opposite to that of the revolution of the 

 satellites. 



If the satellites are arranged as in Fig. 8, where each is 

 more advanced in phase as we go round the ring, the wave will 

 travel in the direction opposite to that of rotation, but if they 

 are arranged as in Fig. 9, where each satellite is less advanced 

 in phase as we go round the ring, the wave will travel in the 

 direction of rotation. 



We may now show these motions of the satellites among 

 each other, combined with the motion of rotation of the whole 

 ring. For this purpose we put in the pin P, so as to prevent 

 the crank axle from turning, and take out the pin Q, so as to 

 allow the wheel E to turn. If we then turn the wheel T, all the 

 small cranks will remain parallel to the first crank, and the 

 wheel E will revolve at the same rate as T. The arm of each 

 satellite will continue parallel to itself during the motion, so that 

 the satellite will describe a circle whose centre is at a distance 

 from the centre of E, equal to the arm of the satellite, and 

 measured in the same direction. In our theory of real satellites 

 each moves in an ellipse, having the central body in its focus, but 

 this motion in an eccentric circle is sufficiently near for illustra- 

 tion. The motion of the waves relative to the ring is the same 

 as before. The waves of the first kind (Fig. 8) travel faster 

 than the ring itself, and overtake the satellites, those of the 

 fourth kind (Fig. 9) travel slower and are overtaken by them. 



% 



This paper was characterised by the late Astronomer 

 Eoyal as " one of the most remarkable applications of Mathe- 

 matics to Physics that I have ever seen." 



6. But notwithstanding the investigations above referred 

 to, and many other original papers on almost every branch 

 of Physical Science, it is for his researches in Electricity and 

 in Molecular Science that Maxwell stands pre-eminent among 

 the men of science of the present century. After taking his 

 degree in 1854, Maxwell read through Faraday's Experi- 

 mental researches, a course which he always recommended his 

 students to follow. In Faraday he found a mind essentially 

 of his own type. Thoroughly conversant himself with the 

 Theory of Attractions as developed in Mathematical Treatises, 



2 L 



