1864.] Da Silveira on the Mean Declination of the Magnet. 347 



talline compound of a somewhat deeper yellow colour, containing probably 



C,H.(NO,)] 

 0,H,0 J 



This substance dissolves in alcoholic soda with a most magnificent 

 crimson colour. Addition of water to the boiling liquid furnishes a yellow 

 crystalline deposit, benzoate (?) of sodium remaining in solution. 



The yellow powder is dinitro-diphenylamine. From boiling alcohol, it 

 crystaUizes in reddish needles, exhibiting a bluish metallic lustre. The 

 analysis of the compound has led to the formula 



Cell. (NO,) I 



H J 



The chemical history of these compounds will be the subject of a special 

 communication. 



XVI. " A Table of the Mean Declination of the Magnet in each Decade 

 from January 1858 to December 1863, derived from the Observa- 

 tions made at the Magnetic Observatory at Lisbon ; showing the 

 Annual Variation, or Semiannual Inequality to which that ele- 

 ment is subject.^^ Drawn up by the Superintendent of the 

 Lisbon Observatory, Senhor da Silveira, and communicated by 

 Major-General Sabine, R.A._, President of the Royal Society. 

 Received June 6, 1864. 



I have much pleasure in communicating to the Fellows of the Royal 

 Society a copy of a Table which I have received from the Superintendent 

 of the Magnetic Observatory at Lisbon, containing the mean values of the 

 Declination in each Decade from the commencement of 1858 to the close 

 of 1863, with corrections applied for the mean secular change, and showing, 

 in a final column, the difference in each decade of the observed from the 

 mean annual value derived from the 216 decades. This Table is a counter- 

 part of Table VII. in Art. XII. of the Philosophical Transactions for 

 1863, p. 292, differing only in the substitution in the Lisbon Table of de- 

 cades for weeks, and the addition of the year 1863. 



This general confirmation by the Lisbon Observatory of the annual 

 variation to which the Declination is subject, " the north end of the magnet 

 pointing more towards the East when the sun is north of the Equator, 

 and more towards the West when the sun is south of the Equator," is very 

 satisfactory. In the Lisbon Table the disturbances have not been elimi- 

 nated. 



