6 POPULAR SCIENCE MONTHLY. 



not sufficient mathematical genius to greatly improve; for thousands 

 of observations made to increase the accuracy of the tables of the 

 motions of the sun and planets; for catalogues of the position and 

 brilliancy of the fixed stars; and last and not least, for keeping the 

 lamp of learning burning in their great schools, or universities, in 

 Spain and elsewhere during the centuries from the eighth to the fif- 

 teenth. Since the time of the Greek schools of Alexandria the home 

 of the exact sciences has been successively in Bagdad, Cordova, Seville, 

 Tangiers, Bokhara and Samarkand. It was only in the sixteenth 

 century that they were firmly domiciled in christian Europe. 



Even in the shortest sketch it is necessary to point out that a great 

 part of the astronomical learning of the Moorish schools was due to 

 Jews; and that it is to orientals and not to Europeans that we owe 

 the earliest recognition of the fundamental truth that all sound pro- 

 gress in astronomy must be based on actual and continued observation 

 of the places of the heavenly bodies; that theory must be based upon 

 practise. It is usual to credit this insight to Tycho Brahe, and it is 

 certain that his greatest claim to our gratitude is based upon a thor- 

 ough recognition of the fact that until observations have shown us 

 exactly how the planets move we can form no adequate theories to 

 account for their motions. But the astronomers of India and Persia 

 in the ninth and tenth centuries thoroughly understood this funda- 

 mental notion, as did Ulugh Beg (1393-1449) at Samarkand, and they 

 invented means to obtain observations of adequate accuracy and in 

 sufficient number. 



The need for more observations and for greater precision was also 

 fully realized by Purbach as early as 1450. Eegiomontanus returned 

 from Italy in 1471 to set up in Nuremberg an observatory for the 

 especial purpose of correcting the Alphonsine tables, which Purbach 

 and himself had found to be so defective a score of years earlier. 

 Landgrave Wilhelm IV of Cassel and his astronomers were working 

 in the same direction in Tycho 's time. It is Tycho 's merit that he 

 was the first in Europe to create instruments of sufficient power, and 

 to use them with exceeding diligence over a long series of years. 

 There was little knowledge in Denmark of what was doing in the 

 orient. Tycho 's plans were made quite independently of the further 

 east. At the same time Europe touched the orient closely, through 

 Venice, and sent many of her sons to study at Moorish schools; and 

 it is not conceivable that Tycho was entirely ignorant of the details of 

 the work done, a century and a half before his time, in Samarkand. 



The debt of Europe to the remoter east has never yet been fully 

 reckoned out. For thirty centuries the culture of the orient has, in 

 one way or another, created, informed or modified our own. The 

 religion, the learning, the art, the architecture of the east have most 



