PRITCHARD S WEDGE PIIOTOMETER 



311 



It 



IS 



obv 



from 



comparison of 



numbers 



table 



th those in 



Table I. that there is a very close agreement between the 



of the two d 



and that the variations in the transmissibility for a unit thickness are depend 



the 



umbers of unit thickness observed 



are system 



To make this fact still 



mor 



ident, we add in Tabl 



d not accidental, 

 isults of the nine 



preced 



series, reduced to a uniform quantity of heat, that is, with the varied 



atmospheric absorption, etc. between the series eliminated. 



TABLE II a. 



No Wedge. 



Wedge 

 at 3 in. 



Wedge 



at 1.8 in. 



Wedge 

 at 3.3 in. 



Wedge 

 at 4 8 in. 



W.-.lge 



atC 3 in. 



1000 



437.4 



200.9 



114.9 



77.8 



56.9 • 



1000 



439.0 



213.5 



122.2 



81.1 



5 7 .3 



1000 



431.3 



2H7.5 



120.7 



80.7 



58.9 



1000 



432.1 



206.9 



118.9 



77.1 



57.9 



1000 



433.2 



196.8 



108.6 



72.4 



52.8 



1000 



406.9 



186.8 



106.0 



70.7 



52.3 



1000 



412.8 



193.3 



109.6 



74.4 



54.4 



1000 



432.1 



197.7 



114.4 



77.0 



55.4 



1000 



432.2 



197.9 



113.1 



75.1 



55.6 



Means 1000 



428.6 ±2.5 



200.1 ±1-9 



114.3 ± 1.3 



76.3 ± 0.8 



55.7 ±0.5] 



The above are th 



me 



of transmission of the total solar beam by 



the Pritchard wedge, each series being reduced separately. 



Taking the mean of all the observations in Tables 

 final values : 



I. and II., we have for the 



No Wedge. 



Wedge 

 at 0.3 in. 



Wedge 

 at 1.8 in. 



Wedge 

 at 3.3 in. 



Wedge 

 at 4.8 in. 



1 Wedge 

 at 6.3 in. 



(a) 714 



305.7 



142.6 



81.4 



54.3 



39.7 



(b) 1000 



428.2 



199.7 

 0.467 



114.0 



76.1 



55.6 



(c) ... 



• • • 



0.570 



0.668 



0.731 



It will be observed that the probable errors above given represent, not or 

 those peculiar to the apparatus, but, what is much more important, the effect of 



changes in the sky during some hours' obse 



If each series were separately 



educed to the form (b), the probable error of the mean would be 



