182 
DBS. A. MATTHIESSEN AND C. VOGT ON THE INFLUENCE OE 
Or writing the above in symbols, 
Po : Pc : : X 100 » : X' 100 ° , .... (1) 
where Po and Pc represent the observed and calculated percentage decrements in the 
conducting-power of the alloy between 0° and 100°, and X, 00 o and X' 100 „ its observed and 
calculated conducting-power at 100°, Pc is, as just stated, equal to 29'307 in nearly all 
cases, the exceptions being with the thallium and iron alloys. 
If the values so deduced be examined, it will be seen that those given in Table XI. 
for the observed and calculated percentage decrement agree very closely with each 
other as well as with the mean value found for the percentage decrement in the con- 
ducting-power between 0° and 100° of the pure metals, viz. 29-307. This is just what 
we expected ; for these alloys conduct electricity, as will be seen from the Table, in the 
ratio of their relative volumes, and therefore their conducting-powers ought to decrease 
between 0° and 100° in the same percentage amount as that of the mean of their com- 
ponents. 
On looking at Table XII., which contains the alloys made of the metals belonging to 
the two classes, we find that, as long as there is no change in the conducting-power of 
the metals lead and tin by the addition of another metal, the conducting-power of the 
alloy decreases between 0° and 100° 29-307 per cent., but the moment the alloys show a 
greater or smaller conducting-power than that of pure lead or tin, then the percentage 
decrement is less than 29-307. Again, the alloys of tin or zinc with copper containing 
small amounts of those metals follow approximatively the above law ; and on referring 
to the curves'* which represent the conducting-powers of these alloys, it would appear 
that, starting with the metal whose conducting-power is greatly altered by a small addi- 
tion of a foreign metal, the above law, as just stated, is approximatively true for all alloys 
as far as the turning-point of the curve, and from this point there is no agreement 
between the observed and calculated values. The difference between these values begins 
to show itself in some cases much sooner than in others ; thus, with tin and copper after 
the addition of one per cent, of the former ; with zinc and copper only after more than 
ten per cent, of zinc has been added, and from these points it gradually increases with 
each addition of metal. What the exact law is which these alloys follow with regard 
to the property under consideration we are unable at present to state, but some of them 
at least show that the law we have put forth will hold good in their cases. Unfortu- 
nately the alloys of this class, containing large percentages of each metal, are exceed- 
ingly brittle and unworkable, so that no complete series of determinations with any set 
of alloys could be made ; had we been able to do this with one or two series, we should, 
in all probability, have found the law which regulates the influence of temperature on 
the conducting-power of this group of alloys. With regard to those in Table XIII. 
very little need be said, for the deduced percentage decrements prove that our law holds 
good for most of the alloys of this group. There are nevertheless a few remarks to be 
* Loc. cit. 
