BLECTROMAGN'ETIC UNIT OF ELECTRICITY TO THE ELECTROSTATIC UNIT. 599 
moving the beam compasses just when contact was complete. A small piece of thin 
sheet steel (about ’03 cm. thick) was interposed between the end of the C}dinder and 
the point of the beam compasses. The compasses were considered adjusted when a 
slight resistance to the motion of the feeling piece was perceived. The beam com¬ 
passes were then placed under the microscopes, and the distance between two definite 
marks on their points determined. The points were then placed close together, so that 
the same resistance to the motion of the sliding piece was felt as in the former case. 
The distance between the marks was then ascertained by means of one of the micro¬ 
scopes and its screw. The distance being so small it seems unnecessary to compare it 
with the divisions of the standard metre. 
Distance between the Marks when the Compasses were Closed. 
Right-hand mark. 
Left-hand mark. 
(1) 
2-.3156 
1-7220 
Mean of 4 ob.servations. 
(2) 
2-1283 
1-5308 
„ 4 
(3) 
2-1287 
1-5200 
,, 5 
(4) 
2-9120 
2-3154 
,, 6 
Giving, as the distance between the marks, T1937 in., or •3032 cm. 
Distance between the Marks when the Compasses were Open. 
Calipers. 
61-3 cm. 
Left-hand screw. 
Riglit-hand screw. 
Left-hand screw. 
Right-hand screw. 
2-1297 
-5698 
2-0656 
■5532 
Mean of 4 observations. 
2-4270 
•2537 
2-3819 
•2415 
5J H 
Giving as the distance betwen the marks when open, 61'3 cm. — '0138 in. 
Hence the length of the cylinder when corrected for temperature equals 60'9784 cm. 
The Distance hetiveen the Inner and Outer Cylinders. 
Since the difference of the mean diameters is only about 1‘09 cm., and since, on 
account of the difficulties of measurement and the irregularities in tlie shape of the 
cylinders, it is impossible to arrive at any satisfactory result by subtracting the mean 
diameter of one cylinder from that of the other, we had to apply some other method. 
We adopted that used in the experiment of 1883, which was to ascertain the amount 
of water required to fill tlie space between the two cylinders This amount was 
determined by weighing. The water employed wms distilled, and was boiled a few 
hours previous to its use to enable it to absorb air bubbles more readily. 
