E.. H. Hall—Rotational Coefficients of Metals. 215 
Art. XXV.—“ Rotational Coefficients” of various Metals ; by 
Epwin H. HAL. 
THE experiments described below were made at the Labora- 
tory of Harvard College during the summer of 1882, and most 
of the results obtained were given at the Montreal meeting of 
the American Association. 
t the York meeting of the British Association, Sept., 1881, 
I gave a list of certain metals with an approximate value of the 
‘‘rotational coefficient ”* for each as determined by my experi- 
ments. ‘This list was published in the report of the Association. 
Several of these metals had, however, been examined in an 
extremely inaccurate manner, as was stated at the time, and the 
numbers assigned them were marked as doubtful. Thus a part 
of the list ran: 
Rotational Coefficient, 
Name of Metal. Arbitrary Scale. 
MBG See ee +15: ? 
Aluminium — 50)" ? 
Manes loos oe .--- —50° ? 
Copper vss) Or. 2 
Brags 73 32 fo. ak — 13? 
es@ CIO. Sho bg: poise No effect discovered. 
Repeating, still in a hasty and rough manner, but more care- 
fully than before, the experiments with all these metals except 
Senden ye and using indeed the same pieces of metal as before, 
found: 
Name of Metal. Rotational Coefficient. 
Zine ghia Tea Sypien +10°5 
Alummiam foe —37° 
ODDOr (olor. oe rine as —' 6'S 
rass Boo he Slee ae 
Lead © 6: ort ese i Noeiiedt discovered, 
It will be observed that the value obtained for brass, which is 
small, is but little changed, but those for zinc, aluminium and 
copper have each been reduced about 25 or 80 per cent. We 
may perhaps by analogy, without actual determination, write: 
Mirena ee —35 
All these values may still be subject to errors of 10 or 20 
per cent, but will nevertheless serve present purposes tolerably 
well, if substituted for those given in the list previously pub- 
lished. Such a list, though rough, may be compared with other 
* Phil. Mag., Sept., 1881, p. 162. 
