and on the Dip of the magnetic Needle, 
3% 
Dipping Needle. 
The dipping needle with which the observations in this 
communication were made, being the same instrument used 
in former observations of the dip, and it having also been 
described by Mr. Cavendish in the Paper before alluded to, 
it will not be necessary to say any thing of its construction 
here. Its situation in the house was in the eastern window 
in the meeting-room, next the door. 
As the observations made with the dipping needle were 
not affected by any other source of error than that of the 
iron work of the room, in order to ascertain the quantity of 
error, the instrument was taken out of doors at two different 
times, after an interval of ten years, differently situated each 
time, and the observations made at both these times out of 
doors, compared with the observations made in the room, 
giving for the error 20' more than the dip was found to be 
in the room, and both agreeing to one minute ; that quantity 
has been added to all the observations made with the dipping 
needle in the room for its error, as affected by the iron work 
of the room. 
