[ 2 | 
Ill. Proposal for a new reproducible Standard Measure of Resist- 
ance to Galvanic Currents. By M. Werner S1eMeEns*. 
[With a Plate. | 
HE want of a generally received standard measure of cur- 
rent resistance, and the great inconveniences thence arising, 
especially in technical physics, suggested to me some years ago 
the experiment I am about to describe. 
My original object was to procure for Jacobi’s stenienar a 
more eeneral introduction into the arts. I soon found, how- 
ever, that this could not be effected without convenience. On 
one occasion, several of Jaccbi’s standards that I had procured 
were so entirely at variance with each other, and their actual re- 
sistances agreed so little with what they ought to have been, 
that I should have been obliged to have had recourse to Jacobi’s 
original measure, only that it was not then at my disposal. In- 
dependently of this, however, I became convinced that a stand- 
ard measure of resistance is only adapted for general use when 
it is easily reproducible. Whether the resistance of a metal wire 
is altered by time, by the shaking of transport, by the passage 
of currents, or by any other cause, isnot yet absolutely decided. 
It is, however, very probable that some such alteration takes 
place, and it is therefore altogether inadmissible to take the re- 
sistance of such a wire as the unit-measure of resistance. More- 
over such standards being copies one of another, as must unavoid- 
ably be the case in the event of their general adoption, their 
deviation from accuracy would be continually mcreasing ; and 
for the purpose of researches which are to be conducted with 
improved instruments and with great accuracy, mere copies 
which are themselves inaccurate are useless. Besides, it would 
be very desirable and convenient to be able to unite a definite 
geometrical conception with the standard measure of resistance, 
which could never be the case with a metallic wire, since the 
resistance of a solid body depends greatly on its molecular state, 
and on the almost unavoidable impurity of the metal. 
The absolute standard measure appeared to me equally ill 
adapted to general use. It can only be reproduced by means of 
very perfect instruments, in places especially arranged for the 
purpose, and by those possessed of great manual dexterity; and 
moreover it is liable to the grave practical objection, that it does 
not exhibit itself in a physical form; and lastly, ae numbers it 
imvolves are exceedingly inconvenient on account of their mag- 
nitude. 
The only practicable method of establishing a standard mea-’ 
sure of resistance which should satisfy all requirements, and 
ee by Mr. I’, Guthrie from Poggendorff’s Annalen, No. 5, for 
