﻿by Change in Angular Velocity. 7 



reduction gears were mounted on a separate table. The 

 cylinders were clamped against a spinning-table which 

 rotated very freely and easily in ball-bearings. Slight 

 want of truth in the centring of the upper end of the 

 cylinder was corrected by hanging a small weight on 

 the rim, or by means of adjusting screws which worked 

 in the rim of: the water-bath and pressed against the 

 cylinder. 



Water-baths, providing a 2-inch layer of water around 

 the sides and base, were fitted to each of the cylinders 

 to make the temperature changes less. These rotated 

 with the cylinder. In the case of: the larger cylinders 

 especially, it was found that without a bath it was im- 

 possible to secure uniform rotation of the water. When 

 the room temperature was rising in the mornings or early 

 afternoons, inward convection currents at the surface 

 carried an excess of angular momentum towards the axis, 

 and the angular velocity at the centre was sometimes for 

 several hours 30 per cent, greater than that of the cylinder 

 itself, the latter being very small. When cooling down, 

 the effect is reversed and the "core" rotates slower than 

 the cylinder. The water-baths made a great improvement, 

 but with the largest cylinder, especially, the water in the 

 bath and in the cylinder had to be mixed thoroughly before 

 each experiment ; and the temperature of the water was 

 regulated with an electric heater to be about o, l C. in 

 advance of the room temperature (when rising). Some 

 experiments lasted for nearly an hour, and a difference of 

 o, l 0. between the temperatures of room and water was 

 enough to start thermal currents having considerable effects 

 (cumulative) on the observations. 



The cleaned surface of the water was lightly dusted with 

 lycopo Hum, " rafts " not being allowed to form. When the 

 temperature was being adjusted with the electric heater, 

 the water was thoroughly mixed by stirring and bubbling air 

 through it. The mean temperature was obtained for each 

 experiment to 0°-01 C. 



At the end of each observation the stop-watch reading 

 (given to 0*1 sec.) was recorded with the angle through 

 which the lycopodium particle had rotated, and the time of the 

 end of the observation as indicated by watch was also written 

 down. A.11 observations in one experiment were made on a 

 selected circle. The cylinder was timed frequently to verify 

 the speed, which was constant to within a per cent, or two, 

 and irregularities were corrected by an adjustable resistance. 



