^4 



Variation of the Compass in Soutk 

 Australia. 



By Charles Hope Haeeis. 



[Eead August 5, 1884.] 



[abeidged.] 



The first information we have as to the variation (declina- 

 tion) of the compass in Sonth Australia is that Flinders, in 

 1802, when off Eucla, crossed a line of no variation — the- 

 needle, which had been pointing west of true north, showed no 

 variation for a short distance, and then pointed east of true- 

 north, the declination increasing as his vessel advanced along, 

 the coast. The first reliable magnetic bearing known to the 

 author is one given by Colonel Light in 1837. It is shown on 

 a plan of the city of Adelaide and surrounding sections, drawn 

 by Arrowsmith, in London. It shows one of the leading survey 

 lines N. 8° 47' W. The true bearing of this line, determined 

 astronomically by the author, is 3° 33', so that the variation in 

 1837 was 5° II' E. In 1841 a Mr. Forrest (of the Eoyal 

 Sappers and Miners) officially recorded the variation as being. 

 5° 9' E. at the north-west corner of the city. In 1850 Mr 

 Painter, well-known as an efficient and painstaking surveyor,, 

 observed the variation at Cape AVilloughby to be 5° 6' E. In 

 1857-9 Mr. Goyder, Surveyor-General, found the variation to 

 be at Mount Eemarkable 5° 39' 13" ; at Mount Serle, 5° 0' 6" ; 

 at Termination Hill, north of Lake Torrens, 5^ 22' 40" ; and 

 near Mount Margaret, about 4° 3' ; so that we have the varia- 

 tion since 1837 fairly well recorded. 



The next question of interest is whether the variation is at 

 present increasing or decreasing, and what the amount of 

 change known as the "annual variation" may be. Dealing 

 first with Arrowsmith's plan, the magnetic bearing of the line 

 given in 1837 as 8° 47' W. is now 9° 15' AV., showing an increase 

 of 28' in 45 years, or at the rate of 36" per annum. 



Taking, next, the variation given by Eorrest in 1841 of 5° 

 9', the mean variation read off by the author on the same spot 

 with three needles has varied from 5° 30' to 5° 43'. These 

 values indicate an increase at the rate of from 30" to 45" per 

 annum. 



During the last six months the author has been systemati- 

 cally recording magnetic bearings in the city of Adelaide, with 

 the following somewhat remarkable result : — The mean aggre- 



