W. Lowery—A Note on Melde’s Eaperiment. 493 
2h 
For small vibrations of the needle, the law MT= =p 2 +6) 
evidently applies; in which 
is the magnetic moment, 
T the force of attraction at a given distance x from the cen- 
ters of the coils, 
t= the time of vibration 
6= the coefficient of torsion of the suspension thread, 
k the moment of inertia of the needle. : 
For the vibrations of the same needle under the influence of 
2 . 
the earth we have—MT, =a eliminating M, z?, &, and 
2 . . 
(1+) we have eat Oh or T=_T,, in which T,, is the force 
z 
of the horizontal component of the earth’s magnetism in abso- 
lute units. We can ne by this method, express the force of 
attraction of a galvanic coil at a given point on its axis where 
the lines of force are sensibly parallel in absolute units. 
No. VI.—A Note on Melde’s Faxperiment ; by W. LOWERY. 
ventral segments with regularity. I have adopted the follow- 
ing method: A glass tube graduated into millimeters 18 
Weighted so as to float in a vertical positio 
that, by drawing off the water from the larger vessel, the dis- 
placement produced by the graduated glass tube is diminished, 
and the tension of the string thereby is 
