370 Mr. Barlow on the effects produced, in the rates of 
The plate and pedestal mentioned in two instances, are the 
same as those described in my “ Essay on Magnetic Attrac- 
tion/’ page 87. See also fig. 3. PI. XXV. of this Memoir. 
The plate was double, one foot in diameter, and weighed 
about 5 lbs. It was placed vertically, and at the distance of 
ten inches from the vertical through the centre of the dial, 
and its centre ten inches below that of the chronometer. 
At the distance of from twelve to fourteen inches from such 
a plate, its action is equal to the mean effect of all the iron 
of a vessel of medium rate, at least on the compass ; as I have 
ascertained by my experiments on board His Majesty’s ship 
Leven and Conway ; and as farther appears from the obser- 
vations of Captain Ross in the Isabella, and of Captain Parry 
in the Hecla. I had, therefore, intended to make farther 
observations on the effect of this plate, had it not been rather 
unexpectedly called away to be fitted on board the Fury, 
with a view of ascertaining its efficacy in correcting the local 
attraction of that vessel in her present interesting voyage. 
