334 H. A. Rowland—Absolute Unit of Electrical Resistance. 
ment of weak currents. It was entirely of brass, except the 
wooden base, and was large and heavy, weighing twenty or 
twenty-five pounds. It could be used with a mirror and scale 
or as a sine galvanometer. It will be necessary to describe 
here only those portions which affect the accuracy of the 
present experimen 
The coils were of the form described above in the theoretical 
porien, and were wound on a brass cylinder about 82 cm 
ong and 11-6 cm. diameter in two deep grooves about 3° em. 
deep and 25 cm. wide. The opening in the center for the 
ale. 
The coils contained about five pounds of No. 22 silk-covered 
copper wire in 1790: turns. 
wo needles were used in this galvanometer, each con- 
structed so that its magnetic axis should be invariable; this 
was accomplished by affixing two thin laminw of glass-hard 
steel, to the two sides of a square piece of wood, with their 
planes vertical. This made a sort of compound magnet very 
strong for its length, and with a constant magnetic axis. The 
first needle had a near] rectangular mirror 2°4 by 1°8 cm. on 
the sides and -22 em. thick. The other needle had a circular 
mirror 2-05 cm. diameter and about 1 mm. thick. The nee- 
dle of the first was 1-27 em. and of the second 1-20 cm. long, 
and the pieces of wood were about -45 cm. and °6 cm. uare 
length of 49 cm. and 42 em. respectively.- The total weights 
were 5-1 and 5-6 grams and the times of vibration about 7° 
