224 Objiervaftovs on fie Direction and Tnlrvstft/ of ihe [Arnii, 



and tlipii, by mo;\ns of n in:Hj;net, causiiiij: it to vibr.iie ihro\ij.»,Ii an an- of 

 60" (i e. 30° oneiilier side of (he stationary position), and noting \\\e 

 sncre>sive diminishing arcs of vibration ot one of he ends ; alter \vhi< h 

 the needle >v.is again centered, and the ar--s of vil)r;ilion of the oilier 

 end si nil I ar'y read o^' t^c. &'('., V hen iliP stationary point was obtained 

 by iiilerpoliition. Thus ui Traiiquebur, Au^Uat Ulh, Needle No. 1. — 



End A Vibrated End B Vibrated 



fiom to 3 — from 



o o o o 



— G3,9 J — 30 9 . 



[ 4- 2/ 0 .-.—2,-5 [ 



— 31,1 — 2S,2\ 



( + 24 2 2,77 



— 2^4 ' — 25,(5 ; 



[ + '^1,6 2, '5 



— 2o,8 —23,2' 



^ 10,2 2,70 [ 



— 23,4 — 20,s\ 



^ -\- IG,9 2,G5 ' 



— 21,0 * ^ 18,5^ 



Mean = —2,72 



and the mean of both readings = 2°, 65 = 2° 39'. 



In this way, five or six readings were genenlly obtained in oach of 

 the eight several positions of the needle, and, in ad 'iiion to this, the 

 readings, when the ntedle had come to rest, vvere likewise ret;istered; 

 thus, in the case just cited, the whole of the readings vvhjii reduced* 

 were as follows : — 





to 

 o 



o 



4- 



21,3 



".-2,G2 





21 7 



2,G0 



+ 



19,3 



2 55 





10,9 



2,55 



+ 



14,6 



2,57 







— 2,53 



Face of Inst, east : axis direct — 3 



west — -H 



■ invd. — 3 



. east — 3 



Reversed the poles 



Readings 

 when at rest. 



I / o 



S5 - 3 

 5 — 3 

 7 — 3 

 20 — 3 



40 

 5 

 15 

 10 



Readings 

 w^hen osciilating, 



O / Of 



-3 4 ~ 3 10 



-2 52 — 2 57 



-3 4 — 3 14 



- 2 43 - 2 35 



* The observations of the noedle when vibrating were read off in degrees and tenths of 

 a degree, in consequence of the lapidityof the vibrations not affording time to register 

 two figures, which genera]!}- would occur in the minutes the enor of reading very 

 rariDly exceeded one-tenth of a degree, or &ix miautes. 



