On the Laws of Absorption of Liquids by Porous Substances. 115 
pure or commercial, varies with an increase of temperature to the 
same degree, which, however, is far from true, and should be - 
borne in mind when constructing a resistance thermometer as 
described by Siemens*. The fourth condition needs no com- 
ment. It is too well known how gold-silver alloys behave when 
exposed to the atmosphere. 
With regard to the expense, the 9 grammes alloy cost, drawn 
into wire, about.£1 4s., but the gold im it is always worth about 
15s. ; so that the real expense is very small. Care must, of course, 
be taken to prevent the alloy coming in contact with mercury, 
which amalgamates readily with all gold-silver alloys. The best 
way to prevent any such accident is to varnish the wires. 
In having this alloy made, it would be advisable always to 
have two made by different parties, so as to be sure no mistake 
has occurred. 
I therefore propose that all those who study the electrical re- 
sistance of metals, should compare one of their metals with this 
alloy, calling its conducting power 100 at 0° (hard-drawn 
wire of 1 millim. length and 1 millim. diam.) ; for then we should 
be able to compare the results obtained by different experimenters 
with one another. ” 
I am sorry that I am not in a position to give the value of 
the absolute resistance of this alloy in terms of Weber’s standard; 
for if this be once determined, we shall, of course, be able to 
reproduce an alloy of known resistance in absolute measure. 
1 Torrington Street, January 1861. 
XVIII. Haperimental Researches on the Laws of Absorption of 
Liquids by Porous Substances. By Tuomas Tatu, Esq. 
[Concluded from p. 65. ] 
we ea following experiments were made with filters of larger 
surfaces. 
Experiment XXIV. 
_ This experiment was made with upward filtration, as in the 
foregoing experiment. ‘The filter was unsized paper, presenting 
a surface of =%ths of an inch in contact with the water. The 
temperature was 43° throughout the experiment, other things 
being the same as in the last experiment. 
The velocity of ascent of the liquid in the filter-tube for the 
first five units was found to be correctly represented by the 
formula h 
ieee 
Towards the close of the experiment, however, it was observed. 
* Phil, Mag. January 1861. 
I2 
