308 Proceedings of the Koyal Society of Edinburgh. [Sess. 
uprights u, u at that the entire system was neutral with respect to 
. When the erector was out of action the system was equivalent to 
a gyroscope mounted freely. In cases where it was desired to provide 
gravity control, small weights were attached to the system in positions 
lying below the plane of the pivot axes. Such weights are shown at . 
Gray Vertical Indicator. 
For many purposes, notably in the construction of vertical indicators 
for use in aircraft, or in the construction of stabilised mirrors for use with 
sextants, no disadvantage is introduced by rotating the stabilised parts. 
In fig. 32 is shown a form of vertical indicator in which the entire pivoted 
system rotates in the direction of spin of the gyroscope g. 
The gyroscope g, as in the previous constructions, is pivoted at PiPi 
(one pivot is indicated in the figure) to a frame /, and this in turn pivoted 
at jppp^io fork F. The fork is mounted on a vertical spindle s which 
