TRANSACTIONS OV SECTION G. 829 



T/ie Theory of Stability, 



An aerodone or aerodrome may be constructed to possess automatic stability 

 without any sp^-cia/ »iecAa?2JS??i for tbe maintenance of equilibrium. The natural 

 flight path is of undulating form, the varieties of flight path obtainable being 

 demonstrated both by theory and by experiment, plottings of these curves being 

 given. 



An extension of the theory gives an equation, termed by the author the 

 ' equation of stability,' and it is shown experimentally that this equation gives the 

 limiting proportions of an aerodone of stable flight path. 



A final consequence of the theory of stability gives the important fact that for 

 any given design of aerodone or flying machine there is a minimum velocity of 

 stable flight, and that the larger the machine the higher this minimum velocity 

 becomes. For a man-baaring maohino it is probably over 30 miles per hour, and 

 in order that a sufficient margin of automatic stability should be provided, the 

 flight velocity should be but little short of 40 ra,h. 



2. Tlie Causes of Wear in Motor Vehicle Machinery.'^ By F. H. Royce. 



3. Clock-driving Meclianism of Equatorials."^ 

 By Sir Howard Grubb, F.E.S. 



The ordinary driving clock for an equatorial generally consists of some form 

 of frictional governor, the best being capable of keeping the rate within about 

 one-fourth to one-fifth per cent., which sufiices for all ordinary observino' or 

 micrometrical purposes ; but for photographic work not only is a higher degree of 

 perfection required but the conditions to be fulfilled are somewhat different. 



All frictional governors tend to correct any error in rate which may from one 

 cause or another have occurred; but in the case of instruments used for photo- 

 graphic purposes it is necessary not only that the rate be corrected, but that the 

 error which has crept in owing to difference of rate having occurred shall be com- 

 pletely wiped out, in order that the star images may be brought back to precisely 

 the same position on the photographic plate which they occupied before the error 

 occurred. 



In order to efiect this an independent free pendulum is used, coutrollino- at 

 every second the rate of the uniform motion clock. 



In the original form of this electrical control, devised by the author, and used 

 for the instruments employed in the International Stellar Photographic Survey, 

 ihe apparatus for effecting this control consisted of three portions, viz., the 

 detector, the distributor, and a pair of correctors for accelerating or retarding, as 

 occasion might require, particulars of which are described in the paper. 



This arrangement produced very perfect results, but was necessarily somewhat 

 complicated, and required very careful adjustment. 



In this paper the author described a modified and simplified form of this 

 control, in which the distributor is altogether dispensed with, the complication 

 very much reduced, and the adjustments simpler. 



It is not claimed that this apparatus gives more perfect results than the 

 original form of control, provided that this latter be in perfect adjustment; but 

 it has been found simpler to work, and gives equally good results, with less 

 liability to go out of adjustment. 



' Published in Engineering, September 18. 



' Reported fully, with illustrations, in Engineering, September 18. 



