Introduction. xi 



1841, to conduct the Observatory, and resigned in April 1842. Mr Russell is, 

 therefore, only responsible for the observations up till that period.* 



During term-days, Mr Russell was assisted by Mr P. Adie of Edinburgh, 

 Mr Hogg of Kelso, and myself. After the April term 1842, Mr DoDS, teacher 

 of Makerstoun parish school, replaced Mr Russell in the term observations ; and 

 after the term 1842, Mr Chisholm, teacher of Maxton parish school, replaced 

 Mr Adie. 



The Daily and Extra Observations, and Observations of Adjustment, till the 

 end of April 1842, were made by Mr Russell, assisted in some of the latter by me. 



MAGNETICAL INSTRUMENTS. 



§ 3. Declinometer. 



7. The Declination Magnetometer was obtained from Grubb of Dublin. The 

 Magnet is 15 inches long, |^ths of an inch broad, and ^th inch in thickness. It fits 

 into a stirrup, whose two eyes receive an axle attached to the suspension thread. 

 At the north extremity, it carries a scale divided on glass ; at the other, about 12 

 inches distant (its focal length), a lens of 1^ inch diameter. 



A marble slab cemented to the top of the Declinometer-Pillar, carries two 

 copper tubes, which are connected at the top by a wooden tie, bearing the Torsion- 

 Circle and Suspension Apparatus. 



The Suspension Thread, formed of sixteen fibres of untwisted silk, is enclosed 

 by a glass tube ; and the Magnet, with copper ring, for checking the vibrations, by 

 a cylindrical box, with glass lids. There are two glazed apertures in the sides of 

 the box, one to the north, where a small mirror throws light upon the glass scale, 

 the other to the south between the Lens and the Reading Telescope. 



The Reading Telescope is fixed to its pier. By noting the coincidences of the 

 Scale divisions with the vertical wire at the eye-glass of the telescope, the variations 

 of the position of the freely suspended magnet are obtained. 



* Mr RtrssELL studied the methods of observing, &c., at Dublin, under Professor H. Llotd, to 

 whom he was also indebted for his attention to various difficulties which were subsequently met with. 

 To Professor Llotd I also owe my acknowledgments for his attention to several of my own com- 

 munications. 



Professor Lloyd, at the desire of Sir Thomas Brisbane, likewise examined the observations made 

 by Mr Russell and by myself till October 1842. 



To Mr Airy, Sir Thomas Brisbane's thanks, and my own, are due, for the facilities afforded 

 me at the Royal Observatory, Greenwich, in April 1842, of acquiring a knowledge of the methods 

 adopted there. I should not omit to mention my obligations to Lieut.-Col. Sabine, and Professor 

 Forbes, for their advice on some occasions. 



