110 THIRD REPORT — 1833. 



could determine the inclination of the needle to the plane of the 

 horizon*. The figure given of the instrument is sufficiently 

 I'ude, but the principles of its construction, as stated by Nor- 

 man, are correct. With this instrument he found the inclina- 

 tion of the needle to the horizon in London to be about 71° 50', 

 but gives no date to the observation, though Bond assigns 1576 

 as the time f . Although in a theoretical point of view it would 

 be desirable to have so early a record of the dip, particularly as 

 subsequent observations lead us to suppose that the dip attained 

 its maximum after this time, yet, considering the uncertainty 

 attending such observations, even with the present improved 

 instruments, we cannot place much confidence in this result, 

 however we may rely upon the author having used every pre- 

 caution in his power to ensure accuracy. Having determined 

 the dip of the needle in London, Norman states that this de- 

 clining of the needle will be found to be different at different 

 places on the earth X, though he does not take a correct view 

 of the subject, for he considers that the needle will always be 

 directed towards a fixed point. 



5. Variation of the Dip. — Subsequent observations by Bond, 

 Graham, Cavendish, and Gilpin, and the more recent ones in 

 our own time, have shown that the inclination of the needle to 

 the horizon at the same place, like the angle which it makes 

 with the meridian, is subject to change ; but the diurnal oscil- 

 lations of the direction are of too minute a character to have 

 been ascertained with the imperfect instruments which we 

 possess. 



This is an outline of the phsenomena hitherto observed, de- 

 pending upon the direction of the forces acting upon the needle. 

 Various attempts have been made to account for those obser- 

 vable at fixed points on the earth's surface at different periods, 

 and also to connect those depending on the different positions 

 of the places of observation, but hitherto with only very partial 

 success. It is not my intention to enter into a detailed history 

 of these attempts, but I may briefly notice some of the most 

 remarkable. 



To Gilbert we are indebted not only for the first clear views 

 of the principles of magnetism, but of their application to the 

 phsenomenon of the directive power of the needle ; and indeed 

 we may say that, with the exception of the recent discoveries, 

 all that has been done since, in magnetism, has for its foundation 

 the principles which he established by experiment §. He con- 



* New Attractive, chap. iii. iv. 



t Philosophical Transactions, 1673, vol. viii. p. 6066. 



X New Attractive, chap. vii. § Gilbert, De Magtiete, ^c, Lond. 1600.. 



