Ross. — On the Declination of the Magnetic Needle. 5 



this phenomenon by myself, I should have been disposed to receive with 

 caution the evidence even of my own senses as to this last fact ; but the 

 appearance conveying precisely the same idea to three individuals at once, all 

 intently engaged in looking towards the spot, I have no doubt that the ray 

 of light actually passed within that distance of us. About one o'clock on the 

 morning of the 23rd February the aurora again appeared over the hills in a 

 south direction, presenting a brilliant mass of light very similar to that just 

 described. The rolling motion of the light laterally was here also very 

 striking, as well as the increase of its intensity thus occasioned. The light 

 occupied horizontally about a point of the compass, and extended in height 

 scarcely a degree above the land, which seemed, however, to conceal from us a 

 part of the phenomenon. It was always evident enough that the most 

 attenuated light of the aurora sensibly dimmed the stars, like a thin veil drawn 

 over them. We frequently listened for any sound proceeding from this 

 phenomenon, but never heard any." 



Now let us see what CajDtain Parry says in reference to the action of his 

 compasses during the continuance of this phenomenon : — ■" Our variation 

 needles, which were extremely light, siispended in the most delicate manner, 

 and, from the weak directive energy, susceptible of being acted upon by a very 

 slight distui'bing force, were never in a single instance sensibly affected by the 

 aurora, which could scarcely fail to have been observed at some time cr other, 

 had any such disturbance taken place, the needles being visited every hour for 

 several months, and oftener when anything occurred to make it desirable." 



I believe that the officer in charge of the Duuedin Telegraphic Station has 

 generally observed, on the day preceding a disjjlay of aurora, a considerable 

 disturbance in the needles attached to his instruments. Those needles are, 

 however, placed under very different conditions to those to which the needle 

 of a declination compass would be subject ; and whilst a current of induced 

 electricity may perhaps (independent of the battery) be directed along the 

 copjier wire, which is in close proximity to the telegraph needle, and in 

 accordance with the established law that " electrical force and magnetic foi'ce 

 are exerted at right angles to each oth^r," deflect it from its normal position, 

 the isolated declination needle may remain unaffected, or affected only in a 

 slight degree. 



In addition to the secular, annual, and accidental variations of the 

 declination, there are also local variations. Within our own Province of Otago 

 there are many such, some of them of a veiy I'emarkable character. 



The secular variation in the " declination" of the needle, as determined 

 from astronomical observations taken on board ship, in the vicinity of our coast 

 line, is stated on the Admiralty charts to be progressing in an easterly direction 

 at the rate of nearly two minutes per annum. 



