CATALOGUE. — TERRESTRIAL MAGNETISM. 



US 



,465 gr. t) 4- .0425 (sin. .03 gr. t) * + .0267 (sin. l.oe 

 gr. 0* ; 'being the number of years elapsed since 1863, 

 the degrees, gr. being decimal. In 1799 the declination at 

 Paris was 2s.26fl", in 183?, according to the formula, it 

 will be a maximum at 24°. 2S'. The complete period is 

 860 years. 



On a magnetic globe floating in mercury. 



Ph. M. XIII. 404. 

 Hitter on magnetism. Gilb. XV. 206. 



Supposes a lunar period. 



Lalande on Churchman's north pole. Ph. M. 

 XIV. 249. 



Account of Gay Lussac and Biot's aerosta- 

 tic voyage. Ph. M. XIX. S74. 



They found little or no difference in the foice at the 

 height of above 4 miles. 



The eruption of Hecla considerably affected the needle. 

 Robison. 



It has been observed, that the variation is certainly 

 affected by atmospherical causes, as in the aurora borealis ; 

 but not certainly by terrestrial, and that it is fair to con- 

 clude that itscause is wholly atmospherical : the argument 

 appears however to be a weak one. 



Table of the change of Declination observed in 

 London. Cavallo. 



Progress of the diurnal Variation. 



Mean diurnal Variation, according to Canton 



Jan. 7' 8" May 13' 0" Sept, 



Feb. . » 58 

 March 11 7 

 April 12 2fi 



June 

 July 



Aug. 



0" 

 13 21 



13 14 



IS 19 



11' 43" 



Oct. 10 30 



Nov. 8 9 



Dec. 6 5 8 



Table of the Dip. Cavallo. 



The mean dip observed by Nairne in London, 1772, was 

 72° 20'. Ph. tr. 1772. 476. 



In 1570, Norman found the dip 71° 50', in 1670, Bond 

 73°47', in 1720, Whiston 75° lo', in 1723, Graham 

 7S^°, or 75°, in 1776 Cavendish malies it 72" 3o': the 

 maximum was therefore about 1720. Ph. u. if 70. 375. 



Magnetical Apparatus. 

 E. M. PI. VIII. Amusemens de physique. 



Artificial Magnetism. 



A. P. Index. Art. Aimant. 

 Reaumur on making magnets. A. ]\ 1723. 

 Marcel. Ph. tr. 1732. XXXVII. 294. 

 Diihamel fa^on d'aimantcr. A. P. 1735. 

 1745. 181. H.I. 



