44 SPECIAL EESULTS IN THE URANOLOGICAL 



vation, if optical means had not been adopted for augment- 

 ing the exactness of the reading commensurately with that 

 of the measurement. The construction of micrometers with 

 fine threads stretched in the focus of the telescope, the ap- 

 plication of which first gave to more exact graduation its 

 peculiar and indeed inestimable value, was devised six years 

 afterwards, in 1640, by the young and talented Gas- 

 coigne. ( 92 ) 



While, therefore, in astronomical researches, telescopic 

 observation and measurement include only 240 years, we may 

 reckon, (without reference to the Chaldeans, Egyptians, and 

 Chinese, and counting only from Timochares and Aristillus( 93 ) 

 to the discoveries of Galileo), more than nineteen centuries 

 in which the position and movements of the heavenly bodies 

 were observed with the naked eye. Seeing the numerous 

 interruptions to which the progress of civilisation and know- 

 ledge among the nations surrounding the Mediterranean was 

 exposed during that long period, we must regard with surprise 

 and admiration the recognition by Hipparchus and Ptolemy 

 of the intricate movements of the planets, of the two principal 

 lunar inequalities, and of the places of the stars; the per- 

 ception, by Copernicus, of the true system of the universe ; 

 and the improvement, by Tycho Brahe, of practical astro- 

 nomy and its methods, all antecedent to the invention of 

 the telescope. Exactness of observation may doubtless have 

 been somewhat increased by the employment of long tubes, 

 used most probably by the ancients and certainly by the Arabs, 

 and arranged so that the object was seen through dioptra or 

 narrow apertures. Abul Hassan speaks decidedly of tubes 

 having eye and object dioptra attached to the extremities; and 

 this arrangement was also employed at the observatory esta- 



