1839] 



in the Madras Light House 



283 



result thus obtained, it should be carefully borne in mind, that each of 

 the S'^ctors laid down in the three figures, represents the angular portion 

 of the horizon throughout which the reflected ini^^ge of some o//<' of the 

 lamps is rendered vi&ib>, by me;iiis of cue of the ref.eciors, and conse- 

 quently, tliat when two or more of these aniular spaces occupy the same 

 part of the horizon, or overlap one another, two or more images will be 

 seen, and so on. 



The object of the arrangement adopted in the 10th fignrp, is, by ex- 

 hibiting the whole of the reflected rays in one view, to j^oint out, both 

 where irregularity in the distribution of the light exists, an 1 also the ex- 

 act quantum of advantage derived from the reflectors in evt-ry separate 

 portion of the horizon, as the number of re^e -ted ima.'-es visible in any 

 particular point of it will of course be shown by the r.uniber of angular 

 spaces of rays, within whose confines it mav happen to be situated. With 

 regard to the first point it wili at once be seen from the figure, that 

 very gr^at int quality in the d'fFnsion of the light prevnils, the whole of 

 the diverging beams apjieaiing to be huddled together ni^cir two points 

 equidistant from the centre of the semi-circumfcriuice*, while that part 

 itself, and the por.ions near the diauieter « 6 (in Fi--;. 15) are in com- 

 parison very scantilv sup})lied. 



As there is some difficulty, owing to the number of lin;'s indispensable 

 to the figure, in distinguishing the angular spaces from one another, and 

 ascertaining the number which lie over any particular \)art, T have in 

 Fig. 20 given another representation of the same semi-cir -umfprence, in 

 which the ditTerently illuminated parts are marked O'f, aud dis* inguished 

 from one another according to the number of ri^flected images vii ib'e 

 within them, and, as the number of degrees of e u-h of these spaces is 

 marked on it, as well as the number of imiges visible tliroavhout it; this 

 figure contains within itself, a condensed view of the whole of the re- 

 sults exhibited in the other four diagrams. 



I have a^so given a tabular form to the contents of the last diagram 

 No. 20, in ordi^.r to a l.nit of a m^^an biing foun 1, an 1 a comparison ma le, 

 with the estimate of the average effect formerly taken. This has been 

 obtained by multiplying the number of images visible in any part of the 

 horizon, by the breadth of the space, expressed in degrees, throughout 

 which that number is seen, anl adding the whole of the pro luots 

 together, and dividing by the number of degrees contained in the entire 

 semicircle: bv this process, and after r-ejecting the first 5| degrees in 



each quadrant represented inFio. 19, in consequence of their falling 



Measuring about 30** on each side, from the point E (of Fig. 15). 



