H. A. Rowland—Absolute Unit of Hlectrical Resistance. 333 
No. 7. 8 and é both ranged over the same portion of the 
scale and so scale error is partly compensated. 
o. 8. The zero-point of all galvanometers was eliminated 
by equal deflections on opposite sides of the zero-point. 
Instruments, 
Wire and coils.—The wire used in all instruments was quite 
small silk-covered copper wire, and was always ound 
accurately turned* brass grooves in which a single layer of 
Wire just fitted. The separate layers always had the same 
number of windings, and the wire was wound so carefully that 
the coils preserved their proper shape throughout. r 
was used between the layers. As the wire was small, very 
little distortion was produced at the point where one layer had 
to rise over the tops of the wires below. Corrections were 
made for the thickness of the steel tape used to measure the 
circumference of each layer; also for the sinking of each layer 
into the spaces between the wires below, seeing that the tape 
measures the circumference of the tops of the wires. The steel 
The advantages of small wire over large are many ; we know 
exactly where the current ; it adapts itself readily to the 
cm. long and its position was read on a circle 20° cm. diam- 
eter, graduated to 15’. The graduated circle was raised so 
that the aluminium pointer was on a level with it, thus avoid- 
ing parallax. The needle and pe only weighed a gram 
or two, and rested on a point at the center which was so nicely 
made that it would make several oscillations within 1° and 
ometer, which was made to order in ; 
before 1 , and much time was lost before finding out the source of the difficulty. 
