Royal Society. 133 



strength of the original liquid ; and it is a fact that in the case 

 of dilute solutions of ammonia, if the same fraction be distilled 

 off, the strength of that fraction is proportional to the strength 

 of the original liquid. I cannot but regard this as a result of 

 extreme importance, and, bearing in mind the immense range 

 over which it holds good, consider that it affords proof that the 

 general march of fractional distillation is as has been represented. 



Putting v=\, let us endeavour to make out the value of v ] 

 from the four experiments. Inasmuch as the quantity of dis- 

 tillate was 50 cubic centims., and the quantity of original liquid 

 was 1 litre, we must multiply the ammonia in the distillate by 

 20 in order that it may be comparable with that in the original 

 liquid. Having done this, we see that the distillate is 9*6 times 

 as strong as the original liquid. If the 50 cubic centims. were 

 an infinitesimal fraction of distillate, then v' would equal 9*6; 

 but the 50 cubic centims. is so large a fraction, that during the 

 evolution of it the liquid has gone down in strength from 1000 

 milligrammes of ammonia per litre to about 547 milligrammes 

 per litre. During the distillation of this 50 cubic centims. the 

 strength of the successive portions of distillate must have varied 

 so that the ratio of the strength of the first infinitesimal to the 

 strength of the last infinitesimal shall be 1000 : 520. The real 

 value of v' is therefore between 13 and 14. 



It is my intention to make determinations of the " coefficients 

 of volatility " of different liquids. 



XVIII. Proceedings of Learned Societies, 



ROYAL SOCIETY. 



[Continued from p. 76.] 



June 13, 1872.— Sir John Lubbock, Bart., Vice-President, in the 



Chair. 



^HE following communication was read : — - 



" On the Spectrum of the Great Nebula in Orion, and on the 

 Motions of some Stars towards or from the Earth." By William 

 Huggins, LL.D., D.C.L., F.R.S. 



In my early observations of the spectrum presented by the 

 gaseous nebulae, the spectroscope with which I determined the coin- 

 cidence of two of the bright lines respectively with a line of nitrogen 

 and a line of hydrogen was of insufficient dispersive power to show 

 whether the brightest nebular line was double, as is the case with 

 the corresponding line of nitrogen. 



Subsequently I took some pains to determine this important point 

 by using a spectroscope of greater dispersive power. I found, how- 

 ever, that the light furnished by the telescope of eight inches aper- 

 ture, to which the spectroscope was attached, was too feeble, even in 



