Manufacture of Compass Needtes. 233 
he instrument. This of course would have an effect upon 
the needle and thus destroy its accuracy. 
To romieny this defect, Mr. Eaton <uiaa the needle to be 
eut off =4 of an inch from each pole, and to be armed at each 
extremity with brass tips ; after which, we are told, the instru- 
ment was = This method seems then to recoms 
mended to general use, as it is said that “‘ another important 
advantage which will attend tipping needles with silver, — 
&c. is that of preserving the points from rust. It has 
demonstrated by conclusive experiments, that magnetism re* 
— Bae in acting most powerfully from the sharp+ 
est i 
: sagaieal ark, that, dlihough it has been rendered proba- 
ble that most metallia bodies possess magnetism, the only sub- 
stance in which it is strikingly and permanently developed, is 
steel; and hence this is altogether employed for the construc- 
tion of magnetic needles: This being the case, my objec- 
tions to Mr. Eaton’s proposed improvement are. 
Ist. That the needle possesses the weight and consequent» 
ly the friction of a long one, with only the magnetic power 
of a short one; it having been sufficiently proved, that the 
friction is nearly proportional to the weight of the needle.* 
2d. That in giz construction of magnetic needles, those 
are the best in which the opposite magnetisms exist in each 
half, gradually i increasing in intensity, from the center to the 
extremities. ut this is not the case when the ends are tipped 
with brass, in which, if any magnetism is developed, it may 
be of another kind from that which exists in the steel to which 
it is attached. Such a needle; therefore, i is liable to 
ject tions: which would apply to one hiav ving consecutive points, 
or which assu other than the ——- 
umes polarity, in parts 
ties.t 
For these reasons, I cannot but think that the method ae 
gested by Mr. Eaton must greatly i impair the directive force 
of the needle, and that its adoption would be injurious rather 
than beneficial; we are therefore at no loss to account for 
the circumstance stated by him, that the needle, when thus 
tipped, was not aflected by magnetic ores, real or imaginary; 
* See Biot, and other authors on magnet 
$A very convenient method of acer tidakng this fact ct, is to detach the nee- 
dle, cover it wit a clean =e of paper, and then sp rinkle on the paper 
ne fine iron filings. an them detect the iii unl exact p 
of poles of the needle. 
VOL XH—NO. 2. 30 ae 
