( ^^^ ) 



i-ou:\\\aic(\ such, thai liiniiiiu' an aiiiilc «tl' ."■>' corrcsiKiiKhMl lo .^O cm. 

 of ihc scah'. l*'r(»iM (hircrciil scM'ies of ohsci'Nalioiis. in which ihe 

 Nai'ialioiis of Ihc dccliiialioii were read from aiiolhcr iiiauiieloiuclci-, 

 it appeared that tuniiim' an aniih^ of -f- -^^^ *»'" -^ IVom the |)(>sili(ni 

 of eipiihhrinni caused a (h'\iati(tn of the niii'i'or from -j- (),()( )! I cm. 

 lo — (),()()2 cm. for one of the niaiiiielomelers and from -|- ( ),()().') c.m. 

 (o — (),()()7 c.m. for the other. (The si,uii -|- indicates that the Inr- 

 iiiji^i>- of the mirror and of tlie niauiielometer are in the same (Hrec- 

 tioii.) Tlios(» nnmliers ai'c the mean \ahies of a series of nsiiallv 10 

 ol)ser\ ations. The needle had a dill'erenl position in (Hfferent obser- 

 vations, either more foreward or more backward: no tixed rehition 

 belwecji the dexiation and the phice of the iieedh' conhl Ite obserx cd. 

 We Iiax'e Cipialed the h)cal iidhience lo /-ei'o : the ei-ror ensinnu' from 

 this will not amount to iiKU'e than to some hnndredlhonsandths. 



A rectan,Liidar turned copper riii<>- <S,4 m.m. lar,L>-e and o,() m.m. 

 Ihick, supporh^l bv a wooden frame formed the circuit of the lanu'cnl 

 ,iial\anomeler, w hicli \\as placed south of llie bililar mau'nelometer. 

 It resembles the apparatus described bv Koni.uMscn AVied. Aim. 15, 

 p. 552, 1S82. 



'J'he circuil of the lanuent i>alvanometei placed to the north was 

 formed bv a coppei- wire of 0,051) cm. dianuMer, ti^htlv sli'ained 

 I'onnd a mai-ble disc; the mauiietomeler can be [daced in a Irianunlar 

 opeiunu'. which is cut out of the disc. 



In ordtM- to (hMermine the local intluence, the ma,i>'nelometei' was 

 supi»oi-led free tVom the othei' |iart of the laniieiit u'ahanomeler and 

 this was tuj'ued o\ei' an anule of 'AO' round it to either side. \Ve 

 found that tiii'uinii' the mai'l>le ,u;d\ juHuneler b-om -{- ,']()'' lo — 'Aif 

 caused a de\iation of tli(^ mirroi' in one series of — 0,00'i cm., 

 another lime of 0,000 cm. For the oilier uahanometer this de\'ialion 

 amounled to -j- 0.004 cm. This (lijferenc(^ mav be asci'ibcd to expe- 

 rimental ei'roi's, and thei'efore no intluence of the instiMimeiil exists 

 here eitiier. 



'Jdie ratio of the values of // al the place where the bitihir maunel, 

 and at those w liei-e the nee(lles of ihe maiiiietometers A\'ere sus|>ended, 

 was detei-mined willi the local-\ariometer of l\oui,K.\rs( ii ; a bitilar 

 \ariometei- indicated the time-xariations of //. 



From the obserxalions w ith the local-\ ari(Hneler — ihe corrections for 



the lime-\ariations beinu' a|)plie(l — Ihe ratio of Ihe values of Ihe inten- 



sitv of Ihe * magnetic Held was derixccl as the axcra^'e \alue of a 



1 

 sei'ies of nundters, whose extreme \alues dilfered h'ss than 



louoo 

 The ratio of // at ihe places of the bililar magnet and of the 



