MAGNETIC SURVEY OF GREAT BRITAIN. 



101 



©f the differences between the computed and observed results. 

 This, substituted in (12), will give the total mean probable 

 error, or the value of e in the equation (17) {rig and w,- now 

 denoting the mean number of observations, and of instruments, 

 at each station) ; and, e and e. being already known, we de- 

 duce the value of e^. 



In addition to the observations of dip already printed in the 

 Irish Magnetic Report, the following pages contain, 1st, a se- 

 ries of observations made by Robert W. Fox, Esq., at nine 

 stations, chiefly in the West of Ireland ; 2nd, observations 

 made by Major Sabine, chiefly in Limerick; 3rd, my own ob- 

 servations in Dublin ; and 4th, a series of observations made 

 by Captain James Ross, at twelve stations, distributed uni- 

 formly over the whole island. 



Mr Fox's observations are contained in Table XXX. They 

 were made in the autumn of the year 1835, at a tinie when the 

 other parts of the Irish survey were in progress ; but, Mr. Fox 

 not being at that time associated in our labours, his results were 

 separately published*. They are now, with his permission, 

 republished in the present memoir. The instrument employed 

 in these observations has been already described f. 



Table XXX. 

 Mr. Fox's Observations in 1835. 



Major Sabine's additional observations, contained in Table 

 XXXI, were made at Limerick, Dubhn, and Bangor, in the 

 year 1836 %. These observations have been already printed 



• Proceedings of the Cornwall Polytechnic Society. 



t Page 3. 



X With the exception of one set of ohservations made with Mayer's needle 

 in the year 1833. These observations, though referred to in the Irish Report, 

 were overlooked in the compilation of the tables. 



