TO FLEEMING JENKIN, Esq.(7)

                                                                                   27th Aug. 1863.

 . . . To compare electromagnetic with electrostatic units:—-   1st, Weber's method.—Find the capacity of a condenser in electrostatic measure (meters). 
Determine its potential when charged, and measure the charge of discharge through a galvanometer.

2d, Thomson's.—Find the electromotive force of a battery by electromagnetic methods, and then weigh the   attraction of two surfaces connected with the two poles.

     3d, (Not tried, but talked of by Jenkin).—Find the resistance of a very bad conductor in both systems—

(1) By comparison with (4th June),
(2) By the log. decrement of charge per second.
All the methods require a properly graduated series of steps.

The 1st and 2d determine V, a velocity = 310,740,000 meters per second.

The 3d method determines V2.

 The first method requires a condenser of large capacity, and the measurement of this capacity and that of the   discharge by a galvanometer.

 I think this method looks the best; but I would use a much larger condenser than Weber, and determine its   capacity by more steps.

The chief difficulty of Thomson's method is the measurement of a very small force and a very small distance. I   think these difficulties may be overcome by making the force act on a comparatively stiff spring and magnifying   optically the deflection.

On the third method we require a very large condenser indeed, also a series of resistances in steps between 4th    June and that of the insulating substance of the condenser, and a galvanometer (or electrometer) to measure    discharge (or tension). . . .