304 



PR1TCHAPJ) S WEDGE PHOTOMETER. 



the mean of the 3, which mean was used as the standard. The observations were all 

 made within li hours of the meridian. November 4th was bright moonlight. There 

 was a slight moonlight during part of the observations of November 1st, but not 

 enough to be troublesome; the background on which the stars disappeared became 

 perfectly black before they vanished, which was not the case on November 4th 

 with stars 4 and 6. These were lost to the eye, while the sky background was still 

 visible in the diaphragm hole. 



Oct. 

 Oct. 



Nov. 

 Nov. 



10 Readings. 



10 Readings. 



10 Readings. 



A x 



r i 



A* 



r a 



A 8 



*• 



in. 



+ 0.410 

 + 0.341 



+0.484 



+ 0.401 



+ .001 

 + .068 

 + .075 

 -.008 



in. 



-0.373 



- 0.529 

 -0.535 



- 0.454 



-.100 



+ .056 

 + .062 

 -.019 



in. 



-0.038 

 + 0.189 

 + 0.062 

 + 0.053 



- .105 

 + .122 

 -.005 

 -.014 



+ 0.409 



±.053 



-0.473 



± .059 



+ 0.067 

 



± .062 



5 Readings. 



5 Readings. 



5 Readings. 



A 4 



r i 



A 6 



r 6 



A 6 



r 6 



in. 



1 • • • • 



-0.767 

 -0.824 

 -0.960 



m • • 



-.083 

 -.026 

 + .110 



±.073 



in. 



-0.497 

 - 0.469 

 -0.322 

 -0.580 



-.030 

 -.002 

 + .145 

 -.113 



in. 



• • • • 



-1.421 

 -1.526 



-1.868 



• • • 



+ .184 

 + .079 

 -.263 



-0.850 



-0.467 



±.072 



-1.605 



±.142 



For some not very obvio 



mean of the thre 



ed 



very much on 



the four nights. 



It was respectively (in wedge-readings) 2.051, 

 2.113, 2.326, and 2.494 inches. It looks very much as if the eye, after practice, 

 became able to follow the star farther before extinction. 



For the first three stars the average deviation of the determination for each night 

 from the mean of the four nights is ± 0.062 in. of the wedge, indicating a probable 



fo 



one 



ght's work of ±0.054 in., and a probable error of half that amount 



for the determination by the four nights' observat 



that 0.7 



Assuming from p 



323 



sponds to one magnitude, the probabl 



mined difference of magnitude between the assumed standard 

 and 3) and either of the first three stars is ±0.04 of a mao-nit 



of the finally deter- 

 (mean of Nos. 1, 2, 

 ide. For star No. 5 



( read 



five times each night instead of ten), it is about ±0.05 of a magnitud 



the swgle-m'f/ht error is 

 on three nights the final 



about the 



same for No. 4, but having been observed only 



ipondingly 



about ± 0.06 m 



The 



probable error for No. 6 is nearly twice as great ; 

 of a good determination by the apparatus used 



obviously too faint to admit 



