140 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
No. 7 (B. & L., ground and polished). 
131-9 div. 
2-8 „ 
40 „ 
2-9 „ 
1-0 „ 
Mean: 132-5 „ 
No. 8 (Zeiss). 
131-4 div. 
1-6 „ 
0-6 „ 
I'l „ 
1-1 „ 
Mean: 131-2 
No. 9 (B. & L., ground and polished). 
132-2 div. 
3-4 „ 
2-2 „ 
2'4 „ 
1-2 „ 
Mean: 132 -3 
No. 10 (No. 1 measured again). 
(No. 1.) 
132 "6 div. 
3- 0 „ 
1- 5 „ 
4- 0 
2- 5 „ 
Mean: 132 -7 ,, 
No. 11 (cover 8/100 mm. in thickness, 
and hence, there being no change of 
the cover correction, had definition). 
132-2 div. 
1-8 „ 
3-1 „ 
2 5 „ 
3-7 „ 
Mean: 132-7 „ 
No. 12 (No. 1 again). 
(No. 1.) 
133 0 div. 
132-3 „ 
1310 „ 
131- 0 „ 
129-5 „ 
132- 5 „ 
Mean: 131 -G 
Mean. 
Difference from 
Mean. 
1. Flat cover 
132-1 div. 
- 0-1 div. 
2 
131-8 „ 
+ 0-2 „ 
3 
131-5 „ 
+ 0-5 „ 
4 
132-1 „ 
-o-i „ 
5 
131-5 „ 
+ 0 5 „ 
G 
131-9 „ 
+ 01 „ 
7. B. & L 
132-5 „ 
- 0-5 „ 
8. Zeiss 
131-2 „ 
+ 0-8 „ 
9. B. & L 
132-3 „ 
-0-3 „ 
10. No. 1, second time .. 
132-7 „ 
-0-7 „ 
11. Cover 8/100 mm 
132-7 „ 
-0-7 „ 
12. No. 1, third time .. 
131-6 „ 
+ 0-4 „ 
Mean of all 12 series .. 
132-0 „ 
Mean of all, excepting the series with the thin cover (No. 11), 
= 131 -9 div. 
Mean of the eight series excluding the three series of measurements 
with No. 1 and the series with the thin cover = 131-9 div. 
Mean of the three series of measurements with No. 1, the flat cover 
= 131-1. 
An inspection of the above measurements discloses the fact that the 
differences from the mean in the case of the three series in which the 
flat cover was used are as great as when other covers were used, and 
