TRANSACTIONS OF THE SECTIONS. 33 



strength for safety agaiii.st breakage ; and tlie author proposes to call it the Crinitl, 

 from'the Latin crinis and ciimtlid. _ 



In the Metre-Tonne-Second System the unit of force, likewise derived hy the 

 (Gaussian method, is 10,000 Crinals, or 100,000,000 Dynes, or is about equal to the 

 gravity of 2 cwt., or of ^o o^' «■ ton. This force would be properly borne as a pull 

 by a iuoderatcly-sized rope ; and the author proposes to call it the Fiiiial, from 

 the Latiji funis and funalis. 



Then we have One Horse-Power, of 33,000 foot-pounds per mmute, about equal 

 to 75,000 Decimetre-Crinals per second ; and the Horse-Power is also about equal 

 to 75 of a Metre-Funal per second. 



Also 1 Metre-Funal = 100,000 Decimetre-Crinals, 



= 10,000,000,000 Centimetre-Dynes, or Erg-s, 

 = 10^" Ergs. 



Also 1 Horse-Power is about = 7,500,000,000 Centimetre-Dynes per second, 

 or as the same may be written 75 X 10^ Centimetre-Dynes per second. 



The number 7,500,000,000, for expressing a Horse-Power under the Centimetre- 

 Gram-Second System, is an exceedingly unmanageable one ; and it gives a very 

 decisive indication that the Centimetre and Gram are too suiall to be suitable as 

 fundamental units of length and of mass for ordinary engineering purposes ; and 

 that there is great need fur the establishment of systems having larger units, such 

 as those which have beeu recommended in the present paper, and for which a con- 

 venient nomenclature has been offered. 



It is to be observed that the provision made by the British Association Com- 

 mittee, in the Eeport already referred to, of a uinhiplo of the Dyne, such as the 

 Megadyne, or million of Dynes, as a larger unit of force, does not accomplish all 

 that is'to be desired, because various important formulas, or convenient methods 

 of statement, will not hold good when any of the units are so derived. Thus, for 

 instance, if the Megadyne be the unit of force, while the Gram and Second are the 

 units of mass and time, the ordinary formulas for giving the so-called " centrifugal 

 force " of a revolving mass, 



F= — and r =nno-r, 

 r 



will not hold good ; and, as another instance, we may notice that the proposition 

 that, in respect to a jet of water, the reaction force on the vessel is equal numeri- 

 cally to the momentum generated per second, will not hold good ; and numberless 

 other instances might readily be cited, but those given may suffice. 



On tlie Preeessional Motion of a Ln^u'td. By Sir W. Thomson, D.G.L., F.B.tS. 



The formulas expressing this motion were briefly explained, but the analytical 

 treatment of them was reserved for a paper " On the Nutation of a Solid Shell 

 containing Liquid." The chief object of the present communication was to illus- 

 trate experimentally a conclusion from this theory which has been announced by 

 the author in his opening address to the Section, to the effect that, if the period of 

 the precession of an oblate spheroidal rigid shell full of liquid is a much greater 

 multiple of the rotational period of the liquid than any diameter of the spheroid is 

 of the diiference between the greatest and least diameters, the preeessional effect 

 of a given couple acting on the shell is approximately the same as if the whole 

 were a solid rotating with the same rotational velocity. The experiment consisted 

 in showing a liquid gyrostat, in which an oblate spheroid of thin sheet-copper 

 filled with water was substituted for the solid fly-wheel of the ordinary gyrostat. 

 In the instrument actually exhibited the equatorial diameter of the liquid shell 

 exceeded the polar axis by about one tenth of either. 



Supposing the rotational speed to be thirty turus per second, the effect of any 

 motive which, if acting on a rotating solid of the same mass and dimensions, would 

 produce a precession having its period a considerable multiple of ^ of a second, 

 must, according to theorj', produce very approximately the same precession in the 

 thin shell filled with liquid as in the'rotating solid. Accordingly the main pre- 



