VII 



CHRISTIAN HUYGHENS 



I 629- I 695 



Christian Huyghens was born at The Hague, April 14, i62p. He 

 studied law in Breda, but becoming attracted to the study of mathe- 

 matics he neglected his legal practice for it. In 1655 he improved 

 the method of grinding telescopic lenses, and, assisted by his brother, 

 discovered the sixth satellite of Saturn and the fact that it was belted 

 with rings. In 16^/ he presented to the States-General the first pen- 

 dulum clock. In i6y8 he evolved his wave theory of light, and pub- 

 lished it at Ley den in i6po. He died at The Hague, lune 8, 16^5. 



THE WAVE THEORY OF LIGHT * 



Proofs in optics, as in every science in which mathematics is applied 

 to matter, are founded upon facts from experience — as for example, 

 that light moves in straight lines, that the angles of incidence and re- 

 flection are equal, and that light rays are refracted in accordance with 

 the law of sines [i. e., that the ratio between the sines of the incident 

 and refracted ray is constant for the same substance.] For this last 

 law is now as generally and surely known as either of the others. 



Most writers in optics have been content to assume these facts, but 

 others more curious have attempted to discover the source and reason 

 of these phenomena, looking upon them as being in themselves interest- 

 ing data. Yet although they have propounded some ingenious 

 theories, intelligent readers still require a fuller explanation before 

 being entirely satisfied. Therefore I herein offer some considerations 

 on the matter with the hope of making clearer this branch of physics 

 which has not improperly gained the reputation of being very obscure. 



I feel myself particularly indebted to those that first began to study 



* Translated from Traite de la Lumiere. 



52 



