( 362 ) 
nected with the secondary wire of an induction-coil, the primary wire of 
which being connected with a Leclanché-cell and oan that microphone 
whose tuning-fork had been made to vibrate. As soon as the needle of the 
electro-dynamometer had undergone a deviation and was nearly in rest 
in that position, the connection with the secondary wire was broken ; 
the needle oscillated around its original zeropoint and by reading 
the turning-points the coefficient of damping was determined in the 
usual manner. It was not possible to determine this coefficient whilst 
the alternating currents were passing through the instrument on 
account of the irregular variations in the intensity of these currents. 
The reader can convince himself of this by calculating K in one of 
the following tables from p, and py or from pz and pz. 
The electro-dynamometer was provided with a concave mirror of 
50 em. focal distance. The lamp-stand and scale differed somewhat 
from that generally used, as is shown in fig. 1. At c an electric 
lamp was placed in the focus of a convex lens, on which a blackened 
vertical diameter had been drawn. The light of the small lamp was 
cast upon the concave mirror a of the electro-dynamometer and 
tence reflected to d. On the scale cd was in the middle the figure 
0; the part of the scale on the right hand of 0 I called +, the 
other —. ab is a normal to the scale passing through the centre 
of the mirror. The scale was not divided into mm. but into smaller 
parts, (a very inconvenient thing in reading) and in such a way 
that 1.59 divisions of the scale were equal to 1 m.m.’). 
During these investigations the electro-dynamometer was 3 times 
removed from its place and every time when again placed provided 
with fresh sulphuric acid. The coefficient of damping, the figure 
where ab cuts the scale and the length of ab (fig. 1) are therefore 
different for the different measurements. They were: 
for the 18 time K =3.3 ab=1830 6= — 220 
sp dn KAD Seb = AT —— — 20 
Peta 3th - K=5.3 ab=1150 b=—202 
The first thing I had to do was to investigate whether I might 
take for granted that with alternate currents of that intensity as 
1) This remarkable lamp-stand was made by Messrs. Narper Bros & Co. London. 
„Theuer und schlecht”, to use the wellknown verdict of Prof. REULEAUX, with a slight 
modification. 
