150 
MINUTES OF PROCEEDINGS OF 
METHOD OP OBTAINING THE DISTANCE OP OBJECTS AT SEA, (PROM 
ELEVATED SHORE BATTERIES), WITHOUT THE USE OP THE SPIRIT- 
LEVEL, AND WITHOUT HAVING TO MARE ANY CALCULATIONS WITH 
TABLES OP NATURAL TANGENTS, Etc. 
By Lieut. H. A. TRACEY, R.A. 
This method, without obtaining the accuracy of the one, suggested by 
Captain Drayson, R.A.,* is still sufficiently good for most purposes; and 
in actual practice from elevated batteries, I have found it give very useful 
results. 
It is only necessary to have a pocket sector and a pair of compasses 
(already in the possession of almost every officer in the regiment) to enable 
the range to be made out from the following data. 
A, height of gun in yds. above the mid-tide level. (Which is that now marked on the 
Ordnance Surveys). 
S, apparent dip of horizon for that height. (A comprehensive table of apparent dips is 
given in the 3rd Vol. Mathematical Course, R.M.A. Appendix, p. 8.) 
The tangent scale of the gun is set as nearly as possible to the angle of 
the dip, and the gun is laid carefully on the horizon, in the direction of the 
target whose range is required. 
The bore is then level. 
Raise the tangent scale until the sights bear on the object. 
We have then the required angle of depression. 
Now measure off, with the compasses, on any scale of equal parts (that on 
the edge of the sector answers best), the number of yards in the height of the 
battery. Open the sector until the transverse distance, on the line of tangents 
(marked T), at the number of degrees and minutes forming the angle of 
depression, is equal to the distance measured on the scale. 
Then, measure with the compasses, the distance between the ends of the 
line (where there is generally a metallic stud let in); 
And you have the required range—as read off on the scale of equal parts 
previously used. 
N.B. Erom experience, I find it better to multiply the very small angle 
of depression by ten, and make the transverse measurement there, when 
of course, the last measurement has also to be multiplied by ten. But being 
taken off a decimal scale, that entails no trouble. 
* Vide page 1. 
