the Viscosity of Aur. 187 
which are observed by means of a gauge. The quantities P,+ P, 
and P,+ P, are obtained as follows :— 
| pean (ee Py oP pl p.(P. = Py oP, 
| §5. Haperimental details. A “tin” can CO (Fig. 2) of about 
10 litres capacity (price 10d.) is used to contain the air. Through 
a well-fitting rubber bung a tube passes, and into this tube are 
i 
Fig. 2. 
soldered a cycle tyre valve V (price 4d.), an ordinary gas-fitter’s 
tap 7 (price 8d.), and a side tube. The side tube is connected 
with the mercury gauge G by a stout rubber tube. The flow 
tube # is connected with the gas tap by a rubber joint. The 
various joints must, of course, be air-tight. 
Air is pumped into the can by means of an ordinary cycle 
pump attached to the valve V, until the pressure is raised to 
