4 Mr DUNLOP'S Account of Observations made in Scotland 



given his own observations, made in Christiania with these 

 needles, in the year 1827, previous to their being sent to Edin- 

 burgh, these observations I have here given, because I consider 

 them connected with mine, as illustrative of the difference of the 

 magnetic intensity between Christiania and Edinburgh as sta- 

 tion points. The time of 300 vibrations is reduced to the 

 temperature of -f 13. 3 REAUMUR, by the formula T T' 

 [1 0.0003711 (t' )], supposing the number of vibrations, at 

 the mean temperature t, to be T seconds, and at the tempera- 

 ture t', to be T' seconds. 



I have accompanied this paper with a table, containing the 

 time which cylinder No. I. required to make 300 vibrations, re- 

 duced to Professor HANSTEEN'S standard cylinder by DOLLOND, 

 the last column of which contains the horizontal intensity at the 

 different stations, that of Edinburgh being taken as unity, and 

 also a chart, on which the time of 300 vibrations of the needle 

 are annexed to the name of the station where the observations 

 were made. 



The lines of equal intensity, or what Professor HANSTEEN 

 calls the isodinamical magnetic lines, are laid down to every five 

 seconds of time ; and I have also copied in dotted lines from 

 HANSTEEN'S chart (lately published), the isodinamical lines ex- 

 tended over Scotland, from his observations in Norway, Sweden, 

 and Denmark. 



It will be seen by comparing these lines, that there is a dif- 

 ference of about 10 seconds in the time of 300 vibrations, be- 

 tween the lines copied from HANSTEEN'S chart, and those dedu- 

 ced from my observations. From this it would appear that the 

 horizontal intensity through Scotland is less than Professor 

 HANSTEEN'S experiments led him to expect. The experiments 

 which I made in Edinburgh, at the back of Captain BASIL 

 HALL'S house, No. 8. St Colme Street, gave nearly the same re- 

 sult with those made behind Coates Crescent by Professor OER- 



