434 



On the present Variation of the Compass. [June 20, 



The body formed in our experiments is thus found to be diazoamidoto- 

 hiol and not azoditolyldiamine, the latter, as before, still remaining to be 

 discovered. Since, in consequence of the operations just mentioned, we 

 had in our possession an appreciable quantity of the diazo body, we were 

 not willing to pass by this opportunity of testing, however cursorily, its 

 action on aromatic monamines. Dyes are in fact produced by treating di- 

 azoamidotoluol with the chlcrhydrates of aniline and naphthylamine in alco- 

 holic solution at 150°C. The numerous by-products, however, which are 

 formed in these processes sufficiently show that the reaction is by no means 

 a simple one. It is more particularly worthy of remark that in its reac- 

 tion with aniline salts no trace of the easily recognizable rosaniline was 

 formed, which might have been the case if the true azoditolyldiamine 

 could have been employed. We have not further studied the products 

 generated in these reactions. 



V. "On the present amount of Westerly Magnetic Declination 

 [Variation of the Compass] on the Coasts of Great Britain, and 

 its Annual Changes." By Staff Captain Frederick J.Evans, 

 R.N., E.R.S., Hydrographic Department of the Admiralty 

 (in charge of Magnetic Department). Received June 15, 18/2. 



(Abstract.) 



The rapidly accelerating value within the last few years of the annual 

 decrease of the westerly magnetic declination over the whole area of the 

 United Kingdom and the adjacent seas, as observed at the fixed magnetic 

 observatories of Greenwich, Kew, Brussels, Paris, and also at Christiania in 

 Norway, is a subject of importance in practical navigation as affecting the 

 compass-bearings derived from charts and those laid down for the guidance 

 of pilots. 



The attention of the Hydrographic Department of the Admiralty ha* 

 been constantly directed to this interesting physical fact; and as the duties 

 of Her Majesty's surveying-vessels employed on our shores between the 

 years 1866 and 1870 embraced nearly the whole extent of coast-line, advan- 

 tage was thus taken, undertone orders of Rear-Admiral" Richards, C.B., 

 F.R.S., the Hydrographer, to determine, with great attention to accuracy, 

 the magnetic declination at widely spread and favourable localities. 



The observations thus made by the surveying officers of Her Majesty's 

 Navy are given in detail, with the corrections for secular change, to the 1st 

 January 1872*, for which epoch a chart of the British Islands, exhibiting 

 the lines of magnetic declination of equal value, is also appended. By com- 

 paring these lines with the corresponding lines given in the Declination 

 chart for 1842'5, Phil. Trans, for 1870, art. xiv., "Contributions to 



* A mean value of 19° 40' being assumed for the westerly magnetic declination at 

 Greenwich Observatory for this epoch. 



