d21 
the temperature falls. Twenty degrees C., has been adopted. 
as a standard temperature, this being near the average: 
temperature of the room where observations are made. If 
the temperature of the room varies more than one or two: 
degrees from that selected for a standard, some arrange- 
ment for maintaining the temperature constant during the 
test is necessary. A wooden vessel, containing a consider- 
able quantity of water adjusted to the proper temperature, 
in which the beaker containing the liquid tested may be: 
placed, answers for this purpose. If the substance under 
examination is one whose coefficient of change for tempera- 
ture is known, any temperature may be taken, and a cor- 
responding correction can be made. 
It is evident that the sensitiveness of the apparatus may 
be increased or diminished to any desired degree, by chang- 
ing the resistance cylinder for one larger or smaller, or by 
changing the wire for one having a different coefficient of 
torsion. It also has an advantage over other methods in 
being applicable for substances having a wider range of vis- 
cosity, and in giving results with different instruments. 
which are strictly comparable. 
In order to better illustrate the use of the apparatus, an 
example is given. 
Scale No. Arc Logarithms- 
reading. of of of 
Degrees arc. oscillation, are. 
bah 1 620.3 2.7296 
65.8 : ; 
625.8 
120.0 3 505.8 2.7040 
577.2 
163.7 5 413.5 2.6165 
538.0 
199.0 T 339.0 2.5802 
The arcs of oscillation given above are for the first, third, 
fifth and seventh arcs, the intermediate ones being omitted. _ 
so as to avoid the use of the same scale reading twice. The 
logarithmic decrement derived from the first and seventh. 
arc 1s 
2.7926—2.5302 
spies RF ilies 04387, 
and from the third aud fifth 
| 2.7040 —2.6165 _ 
2 
The logarithmic decrements found by the two calculations: 
should not differ more than 1 or 2 in the last figure. A 
greater difference would show a considerable erro. in scale: 
reading, and the test should be repeated. Considering this 
decrement as a whole number, we find by referring to the 

0437, 
