10 Archdeacon Pratt on the Figure of the Earthy 



of polarity in general, of which chemical polarity is but another 

 phase. The two phenomena must at least be discussed together. 

 The future investigation of isomerism, as I conceive it, should 

 be carried out in the following order : — First, substances should 

 be examined in order to ascertain the quality of their various 

 parts, — whether, for example, all the chlorine of a chlorinized 

 body could or could not be removed by potassic cyanide*, or the 

 iodine of an iodized body by hydric iodide f — whether a radical 

 did or did or did not part on removal, as is the case with the 

 nitryl of dinitromethylenic chloride already referred to, and with 

 the nitrogen of nitrosaniline J — and so forth. That would be the 

 statical side of the problem. It would next be advisable to de- 

 termine all the conditions, in a known reaction, under which 

 these permanent alterations of function were impressed. This 

 would be the dynamical side of the problem. 



II. On the Figure of the Earth, as obtained from Geodetic Data. 

 By Archdeacon Pratt, M.A., F.R.S. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



IN my last communication to your Magazine I intimated my 

 intention of pursuing the question, which Captain Clarke and 

 I have been discussing, " elsewhere," — my meaning being that I 

 should not only demonstrate the formulae for calculating the axes of 

 the earth on my improved method, but should apply them by re- 

 ducing them to numbers; and as the paper completely worked out 

 would occupy too much of your space, I should endeavour to have 

 it published by one of our scientific societies. I have, however, 

 in vain sought for the leisure to do as I wished, and the desired 

 leisure appears to be further from me than ever. I must there- 

 fore abandon my project of entering into numerical calculations, 

 and satisfy myself with demonstrating the formulae which I 

 think should be used in applying geodetic data to the determi- 

 nation of the earth's mean figure. This demonstration, which I 

 wrote out during a recent voyage, will not, I believe, occupy too 

 much of your space, considering the great importance of the 

 subject. 



2. It is clear that, as BessePs method of applying the principle 

 of least squares to the problem altogether ignores the effect of 

 local attraction at the reference- station of the arc, the method 



* Chem. Soc. Journ. [2] vol. iv. p. 352. 



t Compare Hofmann, Chemical News, vol. ix. p. 163. 



X " On Heating with Soda-lime," Chem. Soc. Quart. Journ. vol. ix. p. 1. 



