Mr. W. J. M. Rankine on the Anomaly-Ruler. 291 



best with the more simple formula Fe 2 Cy 5 NO, 2Na + 4HO. 

 The other elements, viz. the iron, the hydrogen and the ni- 

 trogen, when calculated according to both formulae, so nearly 

 coincide, that the difference cannot be ascertained with cer- 

 tainty by analysis. The amount of carbon appears to me 

 decisive; because, as calculated according to both formulae, it 

 exhibits the greatest difference, and the quantity of carbon 

 found is decidedly in favour of the more simple formula. 



XXXV. On the Anomaly -Ruler - an Instrument to assist in the 

 graphic representation of the place of a Gravitating Projectile 

 in an Elliptic Orbit. By William John Macquorn 

 Rankine, C.E. 9 F.R.S.E., F.R.S.S.A. $c* 



IT may sometimes be desirable, in lecturing on or in dis- 

 cussing the motions of comets, to possess the means of 

 easily and rapidly laying down on a diagram, with as much 

 accuracy as the scale of the drawing will permit, the places of 

 such bodies in their elliptic orbits at given instants of time. 

 The instrument which I shall now describe is intended to 

 facilitate this operation. 



It is simply a thin flat ruler, the form of which is repre- 

 sented by the shaded figure in the drawing, and which may 

 be made of any convenient size. 



The fiducial edge, from C to N, is straight. Those two 

 points ought to be marked by fine transverse lines on both 

 laces of the ruler. From N to I the fiducial edge has the 

 *■ Communicated by the Author. 



U2 



