M A G N E T I C S V I! V E Y O F I' ENNS V L V A Nli ,;, 



I have therefore concluded to apply no temperature correction to the observations 

 in which the old London or the pin weights were used, which m anj case would 

 necessarily be small. 



In Vol. II of the Magnetic and Meteorological Observations at Girard Coll.-,'. 

 we find the following additional observations' (see |>]> 1537-8 1540 1842-3 

 1. ■)!.>):— 



Lloyd Needle No. I. 



July 20, 1843, t = T5 8 = 18°26'.] (position of pin not stated). 



Sept. 5.18-13, 82.8 is 36.0 (pin weight in third hole) 



Lloyd Needle No. 3. 



July 20, 1843, t = T3°.3 * = 21°34'.l (position of pin not stated). 



Ang. 26, 1843, 82.4 21 42.9 (pin weight in third hi 



Sept. 5, 1843, 82.9 21 48.7 



Sept. 12, 1843, C2.fi 21 34.0 



These observations tend to the same conclusion arrived at above. 



Considering the results of 1840 and 1841, and comparing them with those of 

 1843, it seems, upon the whole, preferable to apply no temperature correction for 

 either needle or weight. 



Computation of the Relative and Absolute Total Intensity by Dr. Lloyd's Statical 



Method. 



(See Trans. Royal Irish Academy for 183fi, also Report of the British Association for Advancement 



of Science for 1835.) 



Let h = magnetic dip, 



£ = the inclination of a Lloyd needle when unloaded, 



6 = " " loaded, 



p = ratio of moment of needle to added weight, 



cos £ 

 8 = £ 4- f, sin e = p -j~ sin (£-0), 



d) = total magnetic force, 



8 = a coefficient, 



8 eos 6 . 8 cos 6 ] 



4> = -.- — ,- v - /,., tor any other station A, =— — jz 5-r. 



r sin (p — 6) ; Y sm(d, — ft,) 



Hence for the ratio of total force at any two stations — 



(p eos sin. (<\ — ft,) 



<P\ cos ft,* sin (!) — (/) ' 



cos ft 

 In what follows, the relative total force , —2* was computed for each place 



sin (d — ft) ' ' 



of observation. 



The mean of these values was taken at all the stations where the total force was 



also determined bv the vibrations of the cylinder and bar in connection with the 



dip. 



1 Made about 20 feet from S. R. angle of observatory. 



