326 Prof. F. L. 0. Wadsworth on the Resolving Power of 



the telescope from the slit, d the diameter of the wire, and 

 S the whole length of the slit, we have evidently 



ol~ 2D 'X 



and S _ d b 



a~ D'"'V 



As a check, a few measurements were also taken with the 

 telescope at a fixed distance from the slit, the aperture b being 

 varied until the two elements were just resolved. The effect 



Fig. 3. 



-H — 



a.o 



of varying the brightness of the slits by interposing additional 

 screens and by removing them altogether was also tried, as 

 well as the effect of varying the magnifying power of the 

 telescope. As long as the images were bright enough to be 

 clearly seen there was no appreciable effect produced by 

 either of these changes. The results are presented in the 

 following table : — 



Table II. 



s. 



D. 



d. 



b. 



a I a. ( 



y«. 





1-97 



12760 



0045 



20-5 



2-8 



13 



Sunlight, screened. 



1-46 



12760 







21 



13 



5> >> 



0-97 



12760 







1-35 



13 



)) JJ 



0-60 



9900 







104 



17 



J> !1 



0-36 



6700 







•84 



25 



„ screened and unscreened. 



0167 



4210 







•55 



40 



„ vibration very bad. 



0-150 



3280 







•58 



51 



„ unscreened, cloudy. 



0-100 



2770 



}J 





•37 



60 



jj jj jj 



0075 



2370 







•23 



70 



jj jj jj 



0-250 



11000 



0-20 



26 



•11 



86 



Are light, screened. 



0-500 



11000 



0-20 



170 



•42 



56 



jj jj jj 



