© 
a1 
or 
Prof. R. W. Wood: Some new 
Table of Calibration of Instrument. 






3 | Volts on © Current in . 
| Head: Readings. | Instrument. Standard Resistance. 
| | Amperes. 
Yaa iy O4767 238 
4°38 0628 . 314 
6:48 | 07710 | 384 
115 69326 | 466 
20°2 | “1143 att 
25:3 | 1264 632 
25-9 | Jaoiooes” ae 660 
45°0 | "1630 815 
65°82 2030 1015 
106-1 2662 | 1331 
122°7 / "2890 | 1445 
160:2 | 3384 1692 
| 2065 3936 1968 
| 2581 | 4545 2272 
| 





XLV. Some New Cases of Interference and Diffraction. By 
R. W. Woon, Professor of Hxeperimental Physics, Johns 
\V Hopkins University *. 
\ [Plate XXI.] 
\JN the following paper I propose to discuss certain types 
of the interference of light which have been known for 
many years, as well as some cases which, so far as I know, 
are quite new; the colours of mixed plates and the phenomena 
of interference in transparent films deposited on metallic 
reflectors being the cases chiefly considered. Several years 
ago it occurred to me that it would be worth while io try to 
devise some permanent film which would show Newton’s 
colours under the most favourable conditions, and the cases 
cited in the present paper are, for the most part, the out- 
growth of experiments made in this direction. The facts 
which have been brought out may be summed up as follows. 
The colours of mixed plates are due to diffraction, and 
should not be classed with interferences in thin films. The 
explanation originaily given by Young, and the treatments 
given by Verdet and others, are unsatisfactory, in that they 
do not indicate what becomes of the energy. 
In the cases of films deposited on perfectly reflecting surfaces 
which, according to the elementary theory, should exhibit 
no interference-colours, we may, under certain conditions, 
have colours far more brilliant and quite as saturated as any 
shown by the soap-bubble. In other cases, where at first 
* Communicated by the Physical Society: read January 22, 1904, 
