

Some Spectroscopic Notes. 465 

To find the resolving power: if we consider the inter- 
te i 
ference factor seats Sa, it =O forrn(H+F)=mz7. If m 
sin?(E&+ F) ’ 
be a multiple of x however, then E+F is a multiple of 7 
and we obtain a chief maximum. The minimum adjacent to 
this maximum is then 
ELF- m+ 
ipaltin 

i.e. e(wcos i— cos 6) +f (sin 6 —y sin?) = nal an 
2 
putting 6=pi+ Aé@, for the maximum 
Aé@ (e sin pi+f cos pi) = —A—p(e cos 7 —f sin 2) 
+ (ecosui—fsin pi), . (10) 
and for the adjacent minimum | 
Seah? 3 J 
Aé,(e sin pi+f cos pi) = ae er (é cos i— fsin 2) 
+ (e cos wi—fsin wz). . (11) 
Hence d@;, the angular separation of the maximum and 
minimum, is given by 
a> 3 : r 
d@3(e sini +f cos 7) = —, 
7 
or, since 7 is small, 
dé; = =F 2, Se eee 
By equation (6) d@,, the angular distance corresponding to 
an increase of wave-length dn, is given by 
_ pdrx— ede 
i 
In order that two lines with a wave-length difference dr 
should just appear resolved, d0,;=d8@;, 
dé;= 
‘ Xr 
1. e. _ = pdh—edp. 
: e 
Now p= (u—1) x? 
Se EEE e se on 4. eee 
Phil. Mag. 8. 6. Vol. 7. No. £1. May 1904. 
A (u—1) edr 
‘Mt 
bo 
4 
N 
