796 
MR. H. TOMLINSON ON THE COEFFICIENT OF VISCOSITY OF AIR, 
Set I. 
Diameter in inches. 
Set II. 
Diameter in inches. 
6-026 
6-073 
6-083 
6-010 
6-106 
6-051 
6-106 
6-020 
6-090 
6-030 
6-010 
6-006 
Mean 6'0701 
6-0323 
The circumference of the cylinder was next measured by a steel tape at five 
different equidistant places :— 
Circumference in centims. 
48-64 
48-66 
48-60 
48-56 
48-35 
Mean 48"562 
Allowing for the thickness of the steel tape, the circumference is 48"48 5. 
From the measurements made with the calipers and tape, the mean diameter of the 
cylinder was 15-370 and 15-433 centims. respectively, and the total mean 15-4015 
centims. 
It will be observed that the external diameter is nearly, but not quite, uniform 
throughout; this no doubt arises from the fact that the paper was not quite uniform 
in thickness. Inside, as far as could be judged by inserting a straight edge, the bore 
of the cylinder was perfectly uniform throughout. 
The inside diameter was determined by the calipers at the top and bottom, at eight 
different places in all. It was also determined by gauging the thickness of the walls 
of the cylinder at the top and bottom by means of a wire gauge, and subtracting 
twice the thickness from the external diameter as measured by the tape. The 
internal diameter, measured in the two different ways mentioned above, was exactly 
the same for both, namely, 14"872 centims. The mean of the internal and external 
diameters is 15"1395 centims., and the mean radius 7"5698 centims. 
The length of the paper cylinder was 60"80 centims., and the mass, allowing for 
the air displaced, was 543"6 grammes. 
The wire was inserted into a hole bored in the centre of one end of a vertical brass 
rod 2 millims. thick and 15 centims. long, and there soldered : the other extremity of 
