PEREGRINUS' COMPASS. 179 



during cloudy weather, trie position of the Pole star. It 

 was not combined with any scale, nor was any means pro- 

 vided whereby a vessel could be steered on a given course 

 by the direct aid of the compass itself. In other words, 

 the compass had no "lubber's point" or fiducial line, and 

 the angle of the course to a true north and south line was 

 only guessed at. The nautical astrolabe, however, was 

 fairly well known, and was used for measuring the alti- 

 tude of the sun. It was a ring of metal divided into quad- 

 rants and graduated in degrees. It had cross-pieces, so that 

 there could be pivoted at its center a bar with sight 

 notches at opposite ends. The user held the ring in 

 suspension by his left hand, so that its vertical diameter 

 would be plumb. Then, with his right hand he manipu- 

 lated the sight-bar before his eye, glancing first along it at 

 the horizon line, and then elevating it to the position of 

 the sun, thus rudely measuring the angle of altitude of the 

 sun above the horizon. Peregrinus now combined the 

 nautical astrolabe and the compass, and then, for the first 

 time, he produced a compass having a graduated scale and 

 a fiducial line or "lubber's point," which not only could 

 be steered by, but which could be used for taking the 

 azimuth of any heavenly body. This was very ingen- 

 iously done. He makes his magnet in ovoid form and 

 puts it in a .bowl in symmetrical position. Then, on the 

 upper circular edge of that bowl he places marks, so that 

 a diametral line will coincide with a line passing through 

 the poles of the magnet, which last he has already deter- 

 mined. Then he marks another line at right angles to 

 this, and finally divides the four quadrants into ninety 

 parts each, so that each division is of course one degree of 

 the circle. Now he places the bowl in a large vessel 

 (probably glass) of water, in which the bowl floats, and 

 the magnet, of course, places itself with its poles in the 

 magnetic meridian. Thus he can recognize all points of 

 the horizon by the marks which he has put on the edge 

 of the bowl. Lastly, he rests upon the bowl edge a light 



