522 
PROFESSORS A. W. REINOLD AND A. W. RUCKEB- ON THE 
Table XVI. 
Time. 
Colour. 
Optical 
thickness. 
,! 
Ratio. ' 
li. m. s. 
3 16 0 
Fellow of the second order T (2, 0). 
320 
1-78 
3 17 45 
Green of the second order G (2, 3) . 
301 
1-84 
Later 
White of the first order. 
97 
4T9 
4 23 15 
Red of the second order after the film 
had been thickened. 
388 
1-60 
4 49 0 
White of the first order. 
97 
447 
The numbers given in this Table, combined with the fact that we always get a 
much larger ratio (of which the mean is 5’8), when the film is thin enough to display 
tlie black, are certainly consistent with the view than when the same colour is repro¬ 
duced, the ratio is, at all events, approximately the same, and that, therefore, the 
change in specific conductivity indicated by the value of the ratio is a function of 
the thickness. The connection is further illustrated by the curve on p. 526. 
We now proceed to consider films formed of liquid, to which a metallic salt has 
been added. 
The following Table gives the values of the ratios of the electrical and optical 
thickness as obtained from a number of different films. The numbers are arranged 
in such a way as to bring out the various points which are worth attention. 
Table XVII. 
SolntioDs containing 3 per cent, of KNOobut no glycerine. 
Number of film. 
Date. 
Optical, i.e., true 
thickness. 
Ratio of electrical to 
optical thickness. 
1892. 
Film 2 
July 11 
662 
1-06 
563 
1-07 
.) 
„ 12 
600 
1-03 
545 
1-00 
528 
0-94 
496 
0-93 ! 
429 
1-08 
! 
412 
1-15 i 
.337 
1-24 
305 
1-21 
253 
1-16 ; 
„ 3 
„ n 
320 
1-28 
300 
114 
289 
1-12 
„ 4 
„ 11 
401 
1-22 
307 
1-25 
305 
1-27 
215 
1‘25 
j 
