180 THE INTELLECTUAL RISE IN ELECTRICITY. 



bar of wood. This has, at each end, an upright pin. 

 Normally it is placed in the north and south line. Hence, 

 if he wishes to take the angular bearing of the sun from 

 the north and south line, he moves this bar until the 

 shadows of the pins coincide with the longitudinal axis 

 of the bar; and simply notes the angle between the final 

 direction of the bar and the north and south line marked 

 on the edge of his bowl. To do this he has to hold the 

 bowl steady with one hand, as he describes, and move 

 the bar around its center with the other. Then, of course, 

 he has only to read on his scale the angle between the bar 

 and the north and south line, and he has the solar azi- 

 muth. In a similar way he can find the direction of the 



PEREGRINUS' FLOATING COMPASS. 1 



wind, by turning his bar until it is in line with the direc- 

 tion in which the wind blows. Or, he can find the 

 azimuth of the moon, or a star, by placing his bar in the 

 direction of the heavenly body. Of course it is only a 

 step beyond this, and one that was probably fully known 

 to him, to place the same bar in a line fore-and-aft the 

 ship, and then his instrument would show the course of 

 the vessel. 



The evolution of this instrument from the astrolabe and 

 the old floating compass is obvious ; but Peregrinus is not 

 contented with it, and now he proceeds further, and, for 



1 From Bertelli, cit. sup. 



