1 86 SECTION PHYSICS. 



which had not yet been solved namely, to say what was the true 

 nature of those little bodies which Galileo discovered near Saturn. 

 He first discovered that they were not two, but one body only, and 

 that that one body was a ring. He made that discovery, not with the 

 telescope which is here exhibited, but with one nearly the same. He 

 made more lenses, but not as many as his brother Constantine. The 

 object lens of this old telescope has been made by Christian Huygens, 

 and here is another one. Here also is a lens on which is written the 

 name of Christian Huygens, but it is not genuine. The lenses of 

 the greatest focal length are here in England, and belong to the Royal 

 Society. There is one of 210, another of 170, and one of 120 feet, 

 those lenses however were not made by Christian Huygens, but by 

 Constantine ; but I am happy to add that the lenses of Constantine 

 were as good as those which Christian himself made. We have sent 

 to the Exhibition this planetary, because it was invented by Huygens, 

 and was in fact the first instrument of that kind ever made. 



We have exhibited several instruments invented by 'sGravcsande, 

 not because great discoveries have been made by each of them, but 

 because you find amongst them the first specimens of instruments 

 which were devised to illustrate by experiment discoveries which had 

 been made by mathematical research. It was his object in the first 

 instance to make popular on the Continent the great discoveries of 

 Newton, and he succeeded in fact very well. I think I do not say too 

 much when I say that in his time he was the first lecturer on the 

 Continent. Unfortunately he had to deliver lectures not only on 

 natural philosophy, but on mathematics and on moral philosophy, 

 and that is the reason why he did not make a great number of disco- 

 veries. Some of those instruments have been brought upstairs. For 

 instance, this is an instrument to show that the velocities acquired by 

 falling bodies are to one another as the square roots of the heights. 

 Two little balls are made to roll down a curve, called cycloide, side 

 by side, and one being placed at the height marked 4 and the other at 

 the height marked 16, it is seen that the velocity of the body which 

 has fallen the height of 16 is twice as great as that which has fallen 

 from the height of 4. 



Here is an apparatus which was made to show the properties of 

 centrifugal forces, and it was so good that it is still used every year in 



