E. TOTAL INTENSITY. 



As we have already mentioned, deflection observations were frequently 

 made in connection with the inclination determinations, for the determination 

 of the total intensity. The alhidade on the back of the vertical circle with 

 one or both deflectors screwed in, was set with its zero exactly at the division 

 of the limb that indicated the mean of the inclination readings obtained 

 immediately before, with the same position of the instrument, "Circle E" or 

 "Circle W". A series of readings of both ends of the needle were then 

 taken, first with the needle deflected within one quadrant, and next a cor- 

 responding series with the needle deflected past the vertical. The thermo- 

 meter belonging to the Fox apparatus proved several times to be out of 

 order, and in these cases another thermometer was introduced into the box 

 of the inclination-needle. 



Only in five cases were both the deflectors used together; on all other 

 occasions only the one deflector marked N was employed. 



In analogy with the formula given on page 130, we obtain, as an 

 expression for the total intensity W, 



JMl + ^Q (1) 



sin i// t 



where R t , t and i// t are substituted for R 2 , , and i// 2 , and indicate the 

 corresponding quantities applicable in the case of only the one deflector 

 being employed. No determination of the constants R^ and C t were made 

 either before the voyage, in Hamburg, or after the return, at Wilhelmshaven. 



