372 
DR. J. HOPKINSON ON THE ELECTROSTATIC 
Olive oi\ 
I. 
II. 
III. 
300 
137*7 
3-17 
400 
213-7 
3-16 
500 
319-2 
3-15 
Mean value of K=3"16. 
Castor oil. 
I. 
II. 
III. 
250 
160“2 
4-78 
o 
o 
306-2 
4-79 
400 
319-2 
4-76 
Mean value of K = 4'78. 
Sperm oil. 
I. 
II. 
III. 
300 
132-2 
3-04 
400 
202-7 
3-00 
500 
306-7 
3-02 
Mean value of K=3 - 02. 
Neatsfoot oil. 
I. 
IT. 
III. 
300 
134-2 
3-09 
400 
206-7 
3-06 
500 
311-2 
3-07 
Mean value of K=3'07. 
Turpentine. 
A satisfactory determination for turpentine was not obtained. The turpentine 
seemed to act on the material of the vessel. After being in the condenser a short 
time its insulation was much reduced. When the charge had a potential of about 
GOO elements the condenser discharged itself disruptively through the turpentine. 
However, with a charge of 100 elements on each condenser a balance was obtained at 
228"2, indicating a specific inductive capacitv 2"23. 
The refractive indices were determined from the same samples as the capacities in 
the usual way by the minimum deviation of a fluid prism. The spectrometer was the 
same I had previously used for experiments on glass (Proc. Roy. Soc., 1877). The 
observations were made for the hydrogen lines and the sodium lines, from these the 
