778 Note on the Compass Stars [Sept. 



respectively 77°, 76°, and 74° 49' in the three : — a Lyra, (vega,) is 38° 

 30', 38° 37' and 38° 38' ;— Aldebaran is 11° 15' (? 15° 11'), 15° 43', and 

 16° 11' ;— and a Aquilae 7° 0', 7° 24', and 8° 27 in the Mohit, Mah. 

 Tizini's tables, and the Naut. Aim. for 1839, severally. 



I now proceed to make a few remarks on the fifth section which 

 affords some curious though brief information on the nautical instru- 

 ments of primitive use. I certainly imagined that nothing could be 

 more primitive than my Maldive friend's kamdl — a bit of horn with 

 a knotted string passing through its centre, depicted in fig. 1, PI. 

 XLVIII. of vol. V. when lo ! here is something even less advanced in in- 

 genuity ! Instead of dividing the string and making one board or tablet 

 (loh, ~y) answer for all, it seems to have been an anterior plan to 

 have nine boards differing in diameter one finger (isbdj each ; the low- 

 est having four isbds in breadth; the largest, twelve. These were 

 all strung on one string, as long as the stretch of a man's arm ; and that 

 board was selected in applying the instrument to use, which just covered 

 the space between the star and the horizon. From the passage in the 

 text it is evident that this series of boards was in fact but a substitute 

 for the more primitive employment of the fingers in the measurement 

 of celestial altitude. The fingers had however one advantage, — that 

 stretched at the length of the arm, as radius, they could be placed in a 

 curve, so as to represent equal portions of an arc ; whereas when fingers' 

 breadths were transferred to flat wooden boards they became either 

 sines, tangents or, at the best, chords of the angle measured. It was 

 to correct this (as I imagine) that the string was shortened by the 

 thickness of the board (half an isbd ?) for each successive loh, as 

 they decreased in breadth ; and I have taken the trouble to calculate 

 the effect on data furnished by my own arm and fingers, whence I set 

 down — radius = 27 inches ; and isbd = J inch. The data therefore 

 for each board or loh will be as follow : 



Radius in- 



No. of 



Breadth 



Equal tc 



» Angle 



Difference 



creasing by- 



the loh 



of the loh natural 



deduced. 



or value of 



half an isba 



or 



in inches. 



sine. 





one isba. 



in inches. 



board. 







o / 



o / 



24.04 



1 



3.00 



.1247 



7 10 — 



4 = 1 47§ 



24.41 



2 



3.75 



.1536 



8 50 



1 40 



24.78 



3 



4.5 



.181i> 



10 27 



1 37 



25.15 



4 



5.25 



.2087 



12 3 



1 35 



25.52 



5 



6.0 



.2350 



13 36 



1 33 



25.89 



6 



6.75 



.2607 



15 7 



1 31 



26.26 



7 



7.50 



.2856 



16 36 



1 29 



26.63 



8 



8.25 



.3098 



18 3 



1 27 



27.00 



9 



9.00 



.3333 



19 28 



1 23 







Average of 12 isba 



1° 37' 20" 



