1838.] a Turkish work on Navigation. 773 



sixth, so that eight isbd remain for the elevation. You divide it then 

 in seven parts, throw away one making a knot at the sixth, in which 

 case the elevation of Juddi remains seven isbd. You divide it again 

 in seven (six ?) parts, but you throw none away and make the knot at 

 the end of the yard, in which case there remain six isbd for the 

 elevation. Here the operation ceases ; but all this is calculated on the 

 lowest elevation of Juddi which is the original measure. The way of 

 measuring with the above said thread and table J, is the following: 



first you take the tablet in your left hand, take hold of the first knot 

 with your teeth, stretch forth your hand, don't twinkle with the left 

 eye, and take the elevation so that Juddi is above and the horizon be- 

 low, no more and no less. At this time the arc of elevation between 

 the horizon and Juddi is 12 isbd ; each time that a knot in added an 

 isbd is lessened till at last there remain six isbd, and here ends the 

 operation with the length of the table or bar. If you wish to operate 

 with its breadth it is as follows : at the knot made for the elevation 

 of twelve isbd, that is to say, at the half of the yard the elevation of 

 Juddi according to the measure of the breadth of the table, is again six 

 isbd. Be it known that if you are operating with the breadth and 

 a knot is added, the elevation loses half an isbd, so that it comes 

 at last to three isbd, in which place the northern pole is five isbd. 

 From this place the equator is distant 40 zdm, which makes nearly 

 570 miles and the original measure (.JloJ, *A<V») ls nere at an ena ", 

 because Juddi being in the original measure near the horizon its mea- 

 surement is not just. They call this the original or fundamental mea- 

 sure because Juddi is beneath the pole of the world in the lowest ele- 

 vation opposite to the pole. Besides this they take the measure by the 

 Farkadain, the Naash, and other stars. 



The Sixth Section explains the calculation of the greatest elevation 

 ' of the stars. 



The way is this : you add the distance of the star in the northern 

 quarter to the latitude if it has a northern distance, and you subtract 

 it if it has a southern distance, and the result of the addition or subtrac- 

 tion is the elevation of the star; if it exceeds 90 degrees you throw it 

 away from the half circle and what remains is the greatest elevation ; 

 in the southern quarter the operation is quite the reverse. If you 

 wish to change the degrees into isbd, you know by what has been said 

 that one isbd is 1 « degree, so that it is easy to make out the isbd ; 

 but in order to calculate just the elevation of the stars it is necessary to 

 know to a certainty the distances. Be it known that as the stars move 



