186 



respects, should be placed on the same axis ; and points out how, by 

 means of such a compound needle, both the dip and intensity might 

 be determined by independent methods, so that the agreement of the 

 results would afford a test of the accuracy of the adjustments and of 

 the observations. He considers that the knife-edge support, which 

 has recently been adapted to a dipping needle, would be peculiarly 

 applicable to a needle of this construction. The sensibility of such a 

 needle would be much greater than that of any hitherto constructed, 

 and the utmost delicacy would be required in the adjustments ; but 

 if the needle were accurately constructed, and due care were taken in 

 the magnetizing, and in making the adjustments and observations, 

 the author expects that the dip and intensity would be determined to 

 a degree of certainty hitherto unattained. 



The advantages proposed to be derived from the use of a dipping 

 needle on the principle described in this paper, are, that as the dip 

 would be obtained without inversion of the poles, the results would 

 be less liable to error than when that operation is necessary, and the 

 observations would be made in less than half the time usually re- 

 quired; and that a measure of the intensity of terrestrial magnetism 

 would be obtained from the same observations which give the dip, 

 the intensity of the force being thus always determined by means of 

 the same needle, and at the same instant as its direction. 



April 25, 1833. 



MARK ISAMBARD BRUNEL, Esq., Vice-President, in the Chair. 



A paper was read, entitled, " An Account of an extraordinary lu- 

 minous appearance in the Heavens, seen at Athboy in Ireland, on the 

 21st of March, 1833." By the Right Honourable the Earl of Darn- 

 ley. Communicated by John George Children, Esq. Sec. R.S. 



The noble author's house is situated in lat. 53° 37' N., long. 

 6° 54' W. On the evening of the 21st of March last, at 9 p.m., a 

 stream of luminous matter, reaching from the eastern to the western 

 horizon, which it entered to the north of the constellation of Orion, 

 was observed passing about midway between the Great Bear and 

 Arcturus, and directly over the two principal stars of Gemini. The 

 phenomenon was not accompanied by the usual flashings of an 

 Aurora, but appeared to flow, when attentively observed, in a rapid 

 stream from east to west, and varying in intensity in its course. His 

 Lordship compares it to the stream from the pipe of an engine played 

 over the head of a person standing under it, about the middle of its 

 course. 



The light was most brilliant at the eastern extremity of the arch, 

 where it was about 1° wide, gradually increasing in width and di- 

 minishing in intensity as it approached the western extremity, where 

 it may have occupied about 5° or 6°. Stars of the second and third 

 magnitudes were distinctly visible through the arch, at least from the 

 meridian to the western horizon ; and though not apparently at a 

 great elevation, light clouds occasionally seemed to pass between it 



