MINUTES OF PROCEEDINGS OF 
2 
Suppose G the gun, and S an object at sea, GE the height of the object 
above the sea. Then if UGS be the angle of depression = GSE, 
GS = GE x cosec GSE} 
that is. 
Range = height of gun above sea x cosec of angle of depression. 
The practical application and use of this method will now be considered. 
It is of course of the utmost importance that ranges should be rapidly 
determined, and although processes 1, 2, and 3, would occupy scarcely more 
than three quarters of a minute and to an expert observer not more than half 
as long, still the looking out, and multiplying the cosecant would be a work 
of time, and a proceeding by which errors might arise. To avoid this and 
also to shorten the process, a Table should be printed or written and hung up 
in every battery , that is fifty feet , or more , above low water mark. 
By this means the range in yards could be instantly found by reference to 
the table. 
Tor the purpose of levelling the gun, a common spirit-level should be used, 
and placed in the bore near the muzzle, so as to be easily seen; one gun 
number could watch this, whilst another moved the elevating screw. 
In order to obtain the most correct results, allowance should be made for 
the state of the tide. This would merely require, three columns for range, 
instead of one, the heading for each of these three being, 
Low Water. Mean. High Water. 
These items would affect the multiplier GE merely. 
In order to avoid any possible source of error when referring to this table, 
two lathes of wood might be suspended over the columns of range not being 
used. So that if practice were being carried on at high water, columns 
“ Low water ” and “ Mean ” would be hidden and high water only be that 
visible, and therefore to be used. 
The vernier of the Armstrong gun enables an angle to be read to at least 
•frVth of a degree. If now we suppose that the battery were 100 ft. above 
the sea, we could actually obtain the range by the above method to within 
a few yards. Thus, one minute error would give only about 40 yds. in 2000. 
If, however, the batteries were higher, as they are in many places, the 
amount of error would be slighter. Thus a battery 200 ft. above the sea 
would enable us to obtain the range to within 14 yds. of a mile, an accuracy 
we believe not to be obtainable by any method as simple and practicable as 
the above. 
In many of our coast batteries at home and abroad, the height of the 
gun above the sea is considerable, and therefore this process might be 
there available. In England, there are batteries at Devonport, Eolkestone, 
Shorncliffe, Dover, &c.; and abroad at Malta, Gibraltar, and other places, 
all of which are sufficiently above low water for the range to be obtained 
as above. 
