Page:Philosophical Transactions of the Royal Society A - Volume 184.djvu/349

Current reversed at 4.0 downwards.

⁠Galvanometer.⁠ ⁠Time.⁠ Position. 74 (°).9 06.25 26.9
27.0 = 1.45 centims. per hour. 27.2   72.8 11.30 27.2 12.45 29.2 1.65 centims. per hour. 01.30 30.5 1.70 centims.„ per hour.„ 01.45 30.9

Current upwards.

⁠Galvanometer.⁠ ⁠Time.⁠ Position. 73 (°).9 2.00 30.9 4.15 27.3 1.53 centims. per hour. 73.0 5.00 26.3 1.43 centims.„ per hour.„ 7.15 23.0

Means going up	G. = 73°.9	v = 1.57 centims. per hour.
Means„ going„ down	G. =73°.9	v= 1.60 centims.„ per hour.„
Means of all observations G.		= 73°.9
v		= 1.59 centims. per hour.

We get $\gamma$ from the table of graduations to be ${\frac {1}{255}}$, and find from our equation (p. 346)

$v_{1}={\frac {v\mathrm {A} }{\gamma r}}={\frac {1.59\times .430\times 255}{157\times 10^{9}\times 60\times 60}}=3.09\times 10^{-12}$.

This is for unit potential gradient on the C.G.S. system, and gives for a gradient of 1 volt per centim. a velocity of

$3.09\times 10^{-4}=$ 0.000309 centim. per second.

This is the velocity of the copper ion in a solution of 0.1 grm. equivalent per litre, while Kohlrausch deduced for infinite dilution

0.00031 centim. per second.

The next case I shall describe is that of a pair of salts whose 0.1 grm. equivalent solutions have specific resistances which are nearly the same. Mr. Fitzpatrick kindly supplied me with a long list of conductivities reduced to comparable units,