OR INTERNAL FEICTION OF AIE AND OTHER GASES. 251 



turning the wooden ring in its own plane the receiver can be pressed up against the 

 plate E E. 



F, G, H, K are circular plates of glass of the form represented in fig. 2. Each has a 

 hole in the centre 2 inches in diameter, and three holes near the circumference, by which 

 it is supported on the screws L L. 



Fig. 6 represents the mode of supporting and adjusting the glass plates. L Lis, one 

 of the screws fixed under the plate E E. S is a nut, of which the upper part fits easily 

 in the hole in the glass plate F, while the under part is of larger diameter, so as to 

 support the glass plate and afibrd the means of turning the nut easily by hand. These 

 nuts occupy little space, and enable the glass disks to be brought very accurately to their 

 proper position. 



ACB, fig. 1, is a siphon barometer, closed at A and communicating with the interior 

 of the suspension-tube at B. The scale is divided on both sides, so that the difference 

 of the readings gives the pressure within the apparatus. T is a thermometer, lying on 

 the upper glass plate. V is a vessel containing pumice-stone soaked in sulphuric acid, to 

 dry the air. Another vessel, containing caustic potash, is not shown. D is a tube with 

 a stopcock, leading to the air-pump or the gas-generator. C is a glass window, giving 

 a view of the suspended mirror d. 



For high and low temperatures the tin vessel (fig. 10) was used. When the receiver 

 was exhausted, the ring P was removed, and the tin vessel raised so as to envelope the 

 receiver, which then rested on the wooden support Y Y. The tin vessel itself rested, 

 by means of projections, on the brackets Q Q. The outside of the tin vessel was then 

 well wrapped up in blankets, and the top of the brass plate E E covered with a feather 

 cushion ; and cold water, hot water, or steam was made to flow through the tin vessel 

 till the thermometer T, seen through the window W, became stationary. 



The moveable pai'ts of the apparatus consist of — 



The suspension-piece a, fitting air-tight into the top of the tube and holding the 

 suspension-wire by a clip, represented in fig. 5. 



The axis cdek, suspended to the wire by another clip at C. 



The wire was a hard-drawn steel wire, one foot of which weighed 2-6 grains. 



The axis carries the plane mirror d, by which its angular position is observed through 

 the window C, and the three vibrating glass disks/, g, h, represented in fig. 3. Each 

 disk is 10-56 inches diameter and about -076 thick, and has a hole in the centre '75 

 diameter. They are kept in position on the axis by means of short tubes of accurately 

 known length, which support them on the axis and separate them from each other. 



The whole suspended system weighs three pounds avoirdupois. 



In erecting the apparatus, the lower part of the axis ek is screwed off". The fixed 

 disks are then screwed on, with a vibrating disk lying between each. Tubes of the 

 proper lengths are then placed on the lower part of the axis and between the disks. 

 The axis is then passed up from below through the disks and tubes, and is screwed to 

 the upper part at e. The vibrating disks are now hanging by the wire and in their 



2m2 



