420 
But even in cases, in which the difference is greater, such a plate 
has still some value. For if the obtained results are represented 
graphically, the tensions being taken as abscissae and the values 
a,—a 
ete. as ordinates, we find one point for V, and two for V,. 
) 
The curve must therefore pass through 1 the origin, 2 through 
the point for V,, 3 between the points for V,. If now the values 
a,—a ad,—a Den, 4 fi 
ae and an FR al different from each other, there is a rather 
great distance between the two points found for V,. But at any 
rate we know that the curve must pass between those two points. 
In order to determine other points | took new clouds, which 1 
investigated in the fields V,, V,, V, ete. The second field was 
always equal to that used with the first plate. By measuring the 
_ a'—a_ a,'—a 
distances on the plates, we now obtained the ratios - 
b>" > Shae 
a,'—a En 
ee quantities proportional with these. So we may also make 
aJ—a@ Aj .. 
yer eae if only at the same time the other forms are changed 
) ‘ 
in the same ratio. In this way we might obtain a new point for 
the curve, at least if these considerations are right. In order to 
know this I investigated tivo or more clouds in the same fields, 
successively V,, V,, V, to see, whether the ratio of the double 
refraction in the fields V, and V, was the same. 
Some of these ratios for equal fields are given here. 
ob b Tensions 
1.13; 1.19; 1.14 | = ou eo 
1.54; 1.44 i. atl ay 
os £2365 133 ; “y= 510 mo 
V, = 1900—1970 ,, 
From the rather small-differences I am inclined to conclude, that 
the results with different clouds may be combined to one single curve. 
