308 
straight line corresponding to the weighted 
mean value of the double deflection divided by 
the speed. 
Not long after the first conclusive experi- 
ments on magnetization by rotation were pre- 
sented to the American Physical Society, EKin- 
stein of Switzerland and de Haas of Holland 
described successful experiments on the con- 
verse effect, viz., the production of rotation 
by magnetization, which had been predicted 
and looked for by O. W. Richardson in 1907, 
A 
Y 
c 
MIRROR—---|-~ 
‘TORSION HEAD 
SILK FIBER 
a, COMPEMSATOR . 
seek TO ROTSR 
Bh. 
{BP 
DAMPING VANE 
AND PLATES 
Tet = 
ALUMINUM ROD 
Fig. 
and they have since published additional ex- 
periments. Very recently another inyestiga- 
tidn of this converse effect has been made by J. 
Q. Stewart. All these investigations are in- 
direct but excellent confirmations of the work 
described here. 
In the second investigation, as already 
stated, the method of the magnetometer was 
used. A diagram of important parts of the 
apparatus is given in Fig. 6. 
The rod under test, or rotor, Ff’, was mounted 
with its axis horizontal and normal to the 
magnetic meridian, as in the first investiga- 
tion, and in the second, or equatorial, position 
of Gauss, which offered great advantages over 
the first, or polar, position for this work. 
’ The magnetometer system, which was astatic, 
is shown suspended from the torsion head A by 
SCIENCE 
CONTROL MAGHET 
a eae een Ea 
.--[. UPPER COMPENSATING D 
cons 
[N. 8S. Vou. XLVIIT. No. 1239 
a silk fiber.. To reduce disturbances due to 
variations of the earth’s intensity as much as 
possible, a compensating rod B of the same 
substance and nearly the same size as the 
rotor, was mounted in approximately the same 
position with respect to the upper magnetom- 
eter magnet as that occupied by the rotor with 
respect to the lower magnet. 
Possible errors due to induced currents in 
the rotor and to minute shifts of the rotor’s 
axis in altitude or azimuth were avoided by 
wee - — fee — — Hm em mn we em me ee foe os + Ll 
UPPER 
MAGNET 
c 
E——w 
= LOWER 
MAGNET 
6. 
compensating accurately the earth’s intensity 
with the large electric coil H, as in the earlier 
investigation. © is a small electric coil in 
series with H to make the zero and sensibility 
approximately independent of the compensat- 
ing current in the coil #. t 
The rotors were driven by an alternating 
current motor, operating at the same speed 
in both directions. Three different speeds of 
the rotor could be obtained by using cone 
pulleys. 
The principal magnetometer observations 
consisted in getting the double deflections pro- 
duced by reversing the direction of the rota- 
tion, the speed for the two directions being the 
same. From these readings, the speed, and the 
calibration experiments, H, could be found asa 
@ 
