50 THE HISTORY OF SCIENCE 



tial globes, sextants of large size, quadrants of vari- 

 ous sorts, and contrivances from which in the course 

 of time were developed modern surveying instruments 

 for measuring horizontal and vertical angles. Before 

 the end of the eleventh century an Arab born at 

 Cordova, the capital of Moorish Spain, constructed 

 the Toletan Tables. These were followed in 1252 

 by the publication of the Alphonsine Tables, an 

 event which astronomers regard as marking the 

 dawn of European science. 



Physics and chemistry, as well as mathematics and 

 astronomy, owe much in their development to the 

 Arabs. An Arabian scientist of the eleventh century 

 studied the phenomena of the reflection and refrac- 

 tion of light, explained the causes of morning and 

 evening twilight, understood the magnifying power 

 of lenses and the anatomy of the human eye. Our 

 use of the terms retina, cornea, and vitreous humor 

 may be traced to the translation of his work on op- 

 tics. The Arabs also made fair approximations to 

 the correct specific weights of gold, copper, mercury, 

 and lead. Their alchemy was closely associated with 

 metallurgy, the making of alloys and amalgams, and 

 the handicrafts of the goldsmiths and silversmiths. 

 The alchemists sought to discover processes whereby 

 one metal might be transmuted into another. Sul- 

 phur affected the color and substance. Mercury was 

 supposed to play an important part in metal trans- 

 mutations. They thought, for example, that tin con- 

 tained more mercury than lead, and that the baser, 

 more unhealthy metal might be converted into the 

 nobler and more healthy by the addition of mercury. 

 They even sought for a substance that might effect 



