MR. J. E. H. GORDON ON MEASUREMENTS OF ELECTRICAL CONSTANTS. 429 
ExTRA-dense flint. 
6 = 717 . 
a 2 (2) 1-514 (4) 1-515 (6) 1-511 
a x (1) 1-032 (3) 1-031 (5) 1-030 
a 2 —a i -482 -484 -481 
Mean '48223. 
K= 3-054. 
Light flint. 
6=-6 99. 
a 2 
(1) 1-503 
(3) 1-498 
( 5 ) 
1-495 
(7) 1-500 
a x 
(2) 1-035 
(4) 1-034 
(0 
1-032 
(8) 1-032 
a 2 —a x 
•468 
•464 
•467 
•468 
Mean -46675. 
K = 3-013. 
H ard crown. 
b= '864. 
a 2 (2) 1-621 
(4) 1-617 
(6) 1-616 
(8) 
1-619 
a x (1) 1-032 
(3) 1-032 
(5) 1-031 
(7) 
1-034 
a 2 —a x -589 
•585 
•585 
•585 
Mean 
•586. 
K = 3-108. 
Ordinary plate glass. 
b=- 996. 
a 2 
1733 
1-734 1-731 
<h 
1-043 
1-042 1-042 
a 2 —a x 
•690 
•692 -689 
Mean '6903. 
K —3-258. 
