328 Mr. Harvey’s experimental inquiries relative to the 
be 1 13.55, and of an equal number in the forward part 96.82 ; 
the former exceeding the latter in the ratio of 11.7 to 10. 
To avoid the influence of local attraction as much as pos- 
sible, copper fastenings are commonly employed for a consi- 
derable space round the binnacle. This space however is, in 
most instances, much too confined in its dimensions ; nor is 
sufficient care always displayed by the practical shipwright 
to avoid the mixture of iron and copper.* And to this cir- 
cumstance may be attributed many of the irregularies I have 
noticed, when ascertaining the intensity in the neighbour- 
hood of the binnacle, on board different ships. -f 
To ascertain the influence actually existing in the space 
surrounding the binnacle, was the object of employing the 
concentric circles before alluded to, and of ascertaining the 
intensities at the different stations assumed in their circum- 
ferences. From these it was found, that at nine of the sta- 
tions in the exterior circle, the intensities were greater than 
those at the corresponding stations of the interior circle ; but 
at the other three stations, viz. 2, 6, and 11, they were less. 
* It may not be improper to remark, that although copper fastenings are com- 
monly employed in fixing the planks of the deck, yet the beams which support it, 
being generally composed of two or three pieces, have their scharps secured by large 
iron bolts, at very short distances from each other, and several of which are in the 
vicinity of the binnacle. One cause at least of irregularity in the compass might 
be avoided, by the general employment of copper in the stations round the binna- 
cle. The stanchions also in that part of the vessel should be formed of the same 
metal. 
f Humboldt, in his Voyage across the Atlantic, had much difficulty in disco- 
covering a proper situation for suspending his dipping needle. In his personal Nar- 
ratives he observes, that he finally ascertained a part of the poop to be the best 
place, because it appeared nearly free from iron, and the small portions that existed , 
were very equally distributed 
