﻿and some Applications to Physical Measurements. 481 



Solidity of foundation is a most important requirement. 

 In the experiments of Whiddington*, although the apparatus 

 was set up on a solid base, vibrations of the building even 

 at 2 a.m. proved troublesome. A somewhat similar trouble 

 was experienced in some of the earlier experiments when the 

 apparatus was installed on the top floor of the laboratory. 

 It was found that the vibration of the building caused by 

 people walking about the corridors, and by the passage of 

 heavy motor traffic, appreciably affected the steadiness of the 

 note. Although some of the work was done during the night 

 and over the week end, the trouble always persisted. 



Finally the apparatus was transferred to a room on the 

 ground floor and supported on stone pillars by means of solid 

 rubber pads. The trouble was now completely removed so 

 that successful observations could be made during the day 

 despite the fact that people were continually walking beside 

 the apparatus. 



After lighting the valves, a certain amount of time must 

 elapse before the oscillating system has settled down to a 

 steady state. This initial variation is due to the heating and 

 expansion of the elements of the valves, causing changes in 

 the whole capacity linked with the oscillating systems. In 

 order to save time, thus sparing the high tension batteries 

 and prolonging the life of the valves, the latter were contained 

 in small tin boxes, placed outside the large box, which were 

 lagged with asbestos and cotton -wool. In this way the heat 

 conduction was minimized, and the valves settled down much 

 more rapidly. Other conditions being the same, it was found 

 that certain valves were less satisfactory than others. For 

 some types the settling down process was very long, and by 

 the time the valve was set, other things began to vary. 

 After long trials with " E," " Fotos," and " A. T. " types, 

 it was found that " B " type valves manufactured by the 

 General Electric Company gave most satisfactory results, 

 settling down most rapidly and remaining steadiest. 



The effects of the changes in the elements of an oscillating 

 system on the frequency have been examined by Eccles and 

 Vincent f in the case of wave-lengths of 3000 metres. They 

 determined that between certain limits for each value of the 

 coupling between the plate and grid coils there was a 

 particular value of the filament current for which the wave- 

 length was a maximum. Working at this value of the 

 current it was found possible to hold the beat note steady to 



* Whiddington, loc. cit. 



| Eccles and Vincent, Proc. Roy. Soc. A. vol. xcvi. p. 455 (1919). 



Phil. Mag. S. 6. Vol. 44. No. 261. Sept. 1922. 2 I 



