170 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXX.) 
by the thermometer and the currents in the fluid weaker, so the observations were 
always considered best when made with a standing’ or a falling temperature. 
3399. The following are the actual observations of one series made with the silver 
torsion wire as the temperature fell. The crystal was surrounded by oil. The 
upsetting angle is subtracted as before described (3367.) : — • 
Temp. 
Torsion 
force. 
Temp. 
Torsion 
force. 
Temp. 
Torsion 
force. 
Temp. 
Torsion 
force. 
279° F. 
82 
225° F. 
... 105 
1 90° F. 
... 118 
152° F. 
... 133 
272 
82 
219 
... 117 
186 
... 121 
149 
... 138 
265 
80 
215 
... 117 
183 
... 120 
141 
... 137 
258 
81 
212 
... 105 
180 
... 119 
133 
... 142 
251 
89 
209 
... 107 
177 
... 119 
131 
... 145 
245 
93 
204 
... 108 
173 
... 128 
119 
... 151 
240 
... 97 
199 
... 116 
165 
... 136 
104 
... 160 
235 
... 97 
197 
... 119 
156 
... 134 
92 
... 175 
230 
... 100 
193 
... 119 
It will be understood that each of the numbers under torsion force, increased by 105, 
will give the number of degrees of torsion experimentally observed. The observa- 
tions at 219° and 215° are, 1 have no doubt, influenced by currents; but I kept 
myself purposely ignorant of what might be expected, and I give them as they were 
obtained. When these numbers are laid down on a scale (Plate III. See bismuth 
crystal C), having temperature in one direction and torsion force at right angles to 
it, and when a mean line is drawn through them, it appears to be a straight line; at 
least there is nothing in the results to justify the assej’tion, that the change of force 
at one temperature was different in degree from the change at another, within the 
range employed. The force, as expressed by such a line, was at 100° equal to 162, 
and at 280° it was 77 ; the whole loss within that range being 85, or above half the 
power it possessed at the lower temperature; in other words, an average alteration 
of 4*7 for every 10°Fahr. 
3400. Another set of observations was made with the same bismuth crystal 
surrounded by water. Seventy-one observations were taken between 40° and 207°; 
and, by the substitution of a cold bath, some others were added on for temperatures 
between 5° and 70°, which were in perfect accordance with the former. These, when 
laid down (see Plate III., bismuth crystal A and B), also gave a straight mean line, 
even more close to the various observations than the former one. The force at 5° 
was 168 ; at 270° it was 90 ; at 100° it was 131. The whole change of force between 
5° and 207° is 78, or nearly one-half of the force at 5°; it is at the rate of 3’86 for 
every 10° of temperature, which correspond very closely to the former result ; for the 
rate becomes 4 8 if the force be converted into a scale of number corresponding 
with that of crystal C, 
3401. It is not to be expected (without extreme care) that the numbers in the dif- 
ferent series of observations with the same object should coincide. The variation of 
the medium, which in one case was oil and in the other water, should not, for the 
