162 



instance of attempting to solve' a problem, one of the necessary 

 conditions being omitted. 



The equations found in the second problem, are solved in the third 

 problem, proving that the figure of equilibrium is an ellipsoid. 



3. " Report of a Geometrical Measurement of the Height of the 

 Aurora Borealis above the Earth." By the Rev. James Farquharson, 

 LL.D., F.R.S. 



The principal object to which the author directed the inquiries of 

 which he here gives an account, is the determination by geometrical 

 measurement of the height of the aurora borealis, and of the altitude 

 and azimuth of the point to which the streamers seem to converge, 

 and which has been termed the centre of the corona : these latter de- 

 terminations constituting important data for enabling us to form a 

 clear conception of the whole definite arrangement and progress of 

 the meteor, and also a correct judgement of the degree of reliance 

 to be placed on the methods employed for measuring its height above 

 the earth. The paper is chiefly occupied with the details of the ob- 

 servations made or collected by the author, with their critical dis- 

 cussion, with the correction of some misapprehensions which have 

 existed respecting the views stated by the author in his former 

 papers, and with a reply to the strictures of M. Arago on those views. 



The result of the geometrical measurement of one particular au- 

 rora, gave as the height of its upper edge, 5693 feet above the level 

 of the Manse at Alford ; and the vertex of its arch was found to be 

 14,831 feet northward of the same place. The vertical extension of 

 the fringe of streamers was 3212 feet; leaving 2481 feet for the 

 height of the lower edge above the level of Alford. The tops of the 

 Corean hills, immediately under the aurora, are about 1000 feet 

 higher than that level ; so that the lower edge of the arch was only 

 1500 feet above the summit of that range of hills. 



4. On the Phosphates." By John Dalton, D.C.L., F.R.S., &c. 

 The author takes a review of the labours of preceding chemists 



which bear upon the subject of the atomic constitution of phospho- 

 ric acid, and the salts in which it enters as a constituent ; and shows 

 their conformity with the views he has already advanced on the sub- 

 ject. A supplement is added, giving an account of the effects of 

 various degrees of heat on the salt denominated the pyrophosphate of 

 soda. 



5. " On the Arseniates." By the Same. 



The author here examines the conformity of the results of the 

 analysis of the salts of arsenic with his theory, in the same manner 

 as he has done with the phosphates in the preceding paper. 



6. " On the Constitution of the Resins." Parts II. and III. By 

 J. F. W. Johnston, Esq., F.R.S. 



In this paper the author, pursuing the train of investigation of 



