THE INFLUENCE OF SECONDARY RESISTANCE 89 
The dimensions of that inductorium are as fol- 
lows: 
Primary Secondary 
Length of coil 88 mm. 65 mm. 
Diameter of coil 36 mm. 68 mm. 
Diameter of wire i mm. 0.25 mm. 
Number of turns of wire 300 5000 
Number of layers of wire 4 28 
Resistance 1.5 ohms 300 ohms 
Unfortunately for the general acceptance of these 
dimensions as standard, Kronecker * had, ten years ear- 
lier, proposed his well-known system of units, based on 
determinations made with inductoria having coils twice 
as long as the Berlin coils and each with twice as many 
turns of wire; and with the adoption of his graduation 
the large coils came into common use. By general con- 
sent among physiologists, therefore, rather than by any 
official action, inductoria having coils about 13 cm. long 
and having about 10,000 turns in the secondary are 
recognized as suitable for the uses of the investigator. 
In most well-equipped laboratories such inductoria are 
found, and there seems no valid reason why the general 
dimensions originally selected by Kronecker for his grad- 
uation should not be taken as standard. In a later para- 
graph (p. 92), observations will be cited which show 
that for quantitative work coils of this size are to be pre- 
* Kronecker: Arbeiten aus der physiologischen Anstalt zu Leipzig, 
1871, S. 186. 
