80 



OBSERVATIONS OF ,25IE MAGNETIC INTENSITY 



These results can add nothing to the laboured deductions of the same ele- 

 ment by Professor Lloyd and Major Sabine, but they are important here, as 

 indicating the accuracy with which the corrections for my needles are known, 

 an interval of nine months having elapsed between the observati®ns at Dublin 

 and London. The mean of the three series with the two needles gives 0.936 

 for the horizontal intensity at Dublin to that at London as unity, while the 

 mean of the determinations of the experimenters just referred to is 0.940, the 

 two extremes being 0.946 and 0.934.* 



EDINBURGH. 



The following observations were made at Canaan Park, near Edinburgh. 

 The instrument was much out of order, and required much time and pains to 

 obtain the results, which, after all, are not as accordant as usual: their number 

 probably makes up for the want of close agreement. The numbers in the 

 column of corrected results are reduced for the rate of the chronometer,! as 

 well as for temperature. 



Ohservations for Horizontal Intensity at Edinburgh. 



Needle. 



Date. 



Temp. 



Number 



of 

 Oscill'ns. 



Time of 

 Ten 



Oscill'ns. 



Corrected 

 Time of 



Ten 

 Oscill'ns. 



Mean. 



Coeffic't 



of 



Correction 



for 



Loss of 



Magnet'm. 



Hor. 



Intensity. 



Cylinder. 



(( 



it 

 Bar. 



a 



Year. 



Month. 



D. 



H. 



Fah. ° 



Sees. 



Sees. 



Sees. 



Lond. ] . 



1837 

 1837 



ii 



Feb. 



a 



Feb. 



a 

 11 



.4 



(4 



2 



ii 



4 



2i 



21 



3 



3i 



4 



41 



5 



46 



45 



34 

 33 



441 



250 

 270 

 250 



248 

 250 

 330 



37.05 

 .11 

 .11 

 .08 



40.70 

 .68 

 .75 



37.107 

 40.810 



37.107 

 40.810 



0.986 

 0.995 



0.895 

 0.897 



I do not find in either of Major Sabine's reports, already referred to, a com- 

 parison of the horizontal forces of magnetism at Edinburgh and London. Pro- 



* See Report on the Magnetic Isoclinal and Isodynamic Lines in the British Islands. By Major 

 Edward Sabine. From the Eighth Report of the British Association for the Advancement of Sci- 

 ence. London, 1839. For the early receipt of a copy of this report I am indebted to the author. 



t While at Edinburgh, the main spring of the chronometer gave way, and was replaced by Mr. 

 Bryson. The watch had, subsequently, a very considerable losing rate, but I preferred to submit 

 to this inconvenience to having frequent alterations made in it. 



