THE ROYAL ARTILLERY INSTITUTION. 
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Example. 
In the “ Shoulder of Mutton ” battery, Dover Castle, the height of the 
left-hand gun (110-pr.) is 165*5 ft., say 55 yds. (Dip for that elevation, 
12 ' 20 "). 
Observed angle of depression to target 1° 5O'. 
I measure off 5*5 of the small subdivisions of the scale on the edge of the 
sector, and open the legs until the distance between the points of the com¬ 
pass, and that between the spots marking 18° 20' (viz. 1° 50' x 10) on the 
line of tangents, coincide. Then, taking off with the compasses, the distance 
between the two metallic spots at the end of the line of tangents and 
referring it to the scale on the edge, I find it measures about 16*9 of the 
smaller divisions, I therefore gave the range as 1690 yds. 
In effect, the range calculated by Capt. Drayson's more accurate method 
was 1719 yds. 
This plan can be applied to smooth-bore guns. As with the assistance 
of the sector, the distance on their tangent scales can also be taken off to 
minutes. For instance. 
In the “ East Demi-Bastion,” Dover Castle, whose height above the mid¬ 
tide level is 97 yds. (Dip 16' 10"). The tangent scale was set to the required 
elevation, to level the gun, thus : The sector was opened until the distance 
between the points 60 and 60 on the line of lines (marked Z), coincided with 
the length of one degree on the brass tangent scale (32-pr.). 60 of course is 
chosen as that is the number of parts we wish to divide the degree into. 
The distance between the points 16 and 16, on the same lines, gave the 
required length for 16', which was marked off by the compasses on the brass 
scale. In this case the angle of depression read off, by means of the line 
of lines, was 3° 5', when by the steps described before, the range was 
approximately found, and nearly enough for most purposes. 
A, height of battery measured at the angle multiplied by ten. 
Range, to be read off on the decimal scale and multiplied by the same number as the 
angle. 
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