REVERSED AND NON-REVERSED SPECTRA. 



135 



a =0.0 



A./VXio 3 = o.o 



O.I" 



8.0 



0.2" 

 16.6 



0-3 

 25.6 



0.4 

 34-9 



0-5 



42.7 



0.7 0.8 

 61.7 70.5 



0.9 



78-5 



1.0 

 90.6 cm. 



the mirror M' over the distance AJV along the normal micrometer-screw 

 at n r . The following is an example of the results of corresponding values of 

 AN and A a, when the distance apart of the rays ac and bd was 2^ = 7 cm.: 



0.6 

 50.7 



These results as a whole are much smoother than above, for incidental rea- 

 sons. From a graphic construction the mean rate AA/"/Aa = 0.088 cm. /degree 

 or 5.0 cm. /radian may be obtained. Hence, since 2^ = 7 cm. (&N/Aa)/2R 

 = 0.013 m terms of degrees or 0.72 in terms of radians (table 37). This re- 

 sult is roughly half the preceding, if incidental errors be disregarded. From 

 the above equation, since 1 = 45 nearly, 



AN" 2R 



7-o 



= 5.0 cm. /radian 



Aa 2 cos i 1.41 

 agrees closely with the experimental result. 



TABLE 37. Values of r=A N/A a micrometer displacement 

 per degree of mirror rotation. 



70. Complementary fringes. Some additional attention was now given to 

 the hyperbolic fringes of a fine slit and white light observed when the ocular 

 is drawn outward or to the rear of the position for the principal focus and the 

 spectroscope is removed. They appear and widen with the washed image of 

 the slit. They are quite strong, sharp throughout, and gorgeously colored, 

 the fields and shades, figure 94, a, being nearly complementary in color. The 

 spectrum fringes must be centered if the others are to occur. The former, 

 figure 94, b, are usually long ellipses or hyperbolic with their major axes horizon- 

 tal, while the corresponding new fringes are hyperbolic with the major axes 

 vertical. They are extremely sensitive to rotation of the micrometer mirror 

 about a horizontal axis, rising or falling, but they soon vanish. When the 

 micrometer mirror is rotated around a vertical axis, an operation which sepa- 

 rates the white slit images if originally coincident, the new fringes move 

 bodily by displacement from left to right, or the reverse, depending on the 

 sign of the rotation, while they continually change their color-scheme. When 

 the design is thus displaced as a whole the individual fringes move as shown 



