338 



Distance of objects at sea. 



[Oct. 



Let s and c represent the sine and cosine of the angle 

 QDM=BAM ; and ^=sine of angle AED; AJ' = a; 

 AC = b; ?/;=weight of the body ; then cw =force of the 

 body in the direction g II; also letF denote the force sus- 

 taining the body at E in the direction of the prop DE; 

 then by proposition of the lever AG ; cw—FyXytiYL ; or 

 bciv=aFx; 



Fhcw . . 



= = minimum. 



a X 



which will evidently be so, when ^is a maximum or sine 

 of 90" ; therefore the prop DE must be placed at right 

 angles to AB. Q. E. D. 



in. — Remarks on the method of es^ima. in g the distinice 

 at Sea, from objects of known height. — By C. 



To the Editor of the Madras Journal of 



Lileratiire and Science. 



Sir, 



Allow me to trouble you with a few remarks on the 

 method of estimating the distance at sea, from objects of 

 known height. 



It appears to be of some consequence that a sailor 

 when approaching land, should be able to estimate his 

 distance from objects with the height of which he may 

 be acquainted, such as a Light House, buildings on 

 high ground, or mountains. 



This problem appears for some reason to have been 

 neglected, for I am not aware of any remarks on the 

 subject being published except by Lt. Raper, R. N. in 

 the United Service Journal for 1829, vol. 2d; the for- 

 mula he gives is this. 



Distance in nautical miles = 90° — « — <p where 



sin 0 =r .^.j^r X cos a 



