Prof. Encke oti the Elements of the Planet Ceres. 27 1 



I found that this colouring matter was not removed by boil- 

 ing, nor by filtration through sand and charcoal, but that alum 

 and certain metallic salts, especially when heated with it, threw 

 down a precipitate, and left the water without colour. Of the 

 metallic salts the most effectual appeared to be the sulphate of 

 iron ; a drop of the solution of this salt, boiled with 500 times 

 its bulk of the water, threw down aflocculent, orange-coloured 

 precipitate, and left the water perfectly colourless. I obtained 

 the same results, only much less in degree, when these re- 

 agents were added to the Thames water after its depuration. 



The sediment which was removed from the water by filtra- 

 tion, as mentioned above, appeared to be a heterogeneous mass 

 of various substances, about y^u^^^ ^^ which was siliceous sand ; 

 it also contained a black matter, which gave the whole a dark 

 gray colour, and which was removed by a red heat ; a number 

 of fine fibres that looked like animal down ; and some large 

 fibres probably of vegetable origin : there were also bits of 

 wood, fragments of coal, and small shining particles of a me- 

 tallic nature, which seemed to be sulphuret of iron. The mass 

 indeed consisted of all those substances which were casually 

 introduced into the Thames, and which had not been decom- 

 posed by the fermentative process. They must of course differ, 

 both in quantity and in quality, in every different portion of the 

 water, so as to render it unnecessary to attempt a more minute 

 examination of them : in the present instance, the sediment, 

 when completely dried at a temperature of 200°, was in the 

 proportion of about 9 grains in 10,000 grains of the water. 



XXXVIII. On the Elements of the Planet Ceres. By Pro- 

 fessor Encke *. 

 SINCE the completion of the first calculations for newly 

 determining the orbit of Ceres, one of my respected astro- 

 nomical friends has given me the hope that the investigations 

 on this subject will be more completely and more accurately 

 performed by another hand. It will therefore be sufficient 

 in this place to explain the ground-work of my determination, 

 in order the better to form an estimate of the confidence to 

 which the places derived from it are entitled. 



The perturbations were developed in the same manner as 

 for the other small planets, in regard to the elements them- 

 selves, and not to the places of the planets in space. A review 

 of the last determination of Professor Gauss (Zach's Monthly 

 Correspond. 1809, May,) on which all places of the planet 

 hitherto given were founded, and some trials made at the latest 



• From tlic Astrinwmischcf Jahrbuch fiir 18.31, p. 275. 



opposi- 



