90 



OBSERVATIONS OF THE MAGNETIC INTENSITY 



made by Keilhau and Boeck, and which give the total intensity at Vienna, as 

 compared with Paris, 0.983, differing from the above only 0.006. 



The numbers for the horizontal intensity furnished by the two needles some- 

 times, as in this particular case, differ; and, in general, the greater relative in- 

 tensity is given by the bar needle. After an examination of various causes 

 which suggested themselves as likely to produce this result, I am still at a loss 

 to explain it. It is not due to an ill-ascertained correction fOr the loss of mag- 

 netic force, nor for temperature, nor to a want of horizontality in the magnetic 

 axis of the needle. The mode of observing- renders the limits of error in the 

 separate sets of observations much below these differences. It was my prac- 

 tice in observing to employ the cylinder needle which has a very small cor- 

 rection for temperature first, and, mean while, to place the other in the shade, 

 so as to avoid an error from its not having acquired the temperature of the sur- 

 rounding air. 



TRIESTE AND VENICE. 



The observations at Trieste were made in the Botanical Garden, and those 

 at Venice in the garden of the Armenian Convent, on the Island of St. La- 

 zarus. 



Observations at Trieste and Venice. 



For Horizontal Intensity. 



Flace. 



Needle. 



Date. 



Temp. 



No. of 

 Series. 



No. of 

 Oscill'ns. 



Time of 



Ten 



OsciU'ns 



at 60°. 



Coeffic't 



of 

 Corr'n 



for 

 Loss of 

 Magn'm. 



Horizontal 

 Intensity. 



Year. 



Month. 



D. 



H. 



Fah. ° 



Sees. 



Paris 1. 



Trieste 



Cylinder 

 Bar 



1838 



April 



4 



11 



101, A.M. 

 Ill, " 



54.0 

 54.5 



2 



2 



700 

 580 



32.889^ 

 35.426 



1.0091 

 1.0024 



Mean, 



1.121 

 1.135 



1.128 



Venice 



Cylinder 

 'Bar 



1838 

 (I 



April 



11 



(1 



12i, P. M. 



67.5 

 67.6 



2 

 2 



700 

 700 



32.876 

 35.393 



1.0097 

 1.0029 



Mean, 



1.122 

 1.137 



1.129 



For Dip, 







Trieste, 1838, April 4lh, Needle No. 1, 63° 19'. 1 



No. 2, " 22.5 



Mean, 63° 20'.5 





Venice, 1838, April llih, Needle No. 1, 63° 18'. 9 



No. 2, " 24 .9 



Mean, 63° 21'.9 





Total Intensity at Trieste, compared with Paris as 

 " " Venice, " " " 



unity, 0.970. 

 "' 0.9715. 





