Capt. Parry and Lieut. Foster's observations ,&c. 327 
7. A plain rectangular needle, of the same length as 
No. 6, and used in the same instrument ; but em- 
ployed exclusively for the intensity. 
It may not be unnecessary to state, that every precaution 
which suggested itself was taken to insure accuracy, and 
that the needles were vibrated after each observation, by 
means of a small piece of magnetised wire, that their axis 
might not be injured by raising them in the Y' s off' the agate 
planes. 
Each of the registered observations on the dip, were 
deduced from five readings of the needle, in each of its 
different positions. 
The observations for intensity, by means of the time in 
which the needles performed one hundred vibrations in the 
meridian, are deduced from the mean of four hundred vibra- 
tions, obtained with the face of the instrument on each side 
of the vertical, and the needles reversed on their axis, in the 
two positions. 
