168 Mr. W. Galbraith's Remarks on the Experiments 



Again, from these errors we see that the greatest deviation 

 takes place at Formentera, and the next at Bordeaux with 

 contrary signs. Indeed the length of the pendulum by ex- 

 periment diminishes from Figeac to Bordeaux ; whereas, since 

 die latitude of Bordeaux is greater than that of Figeac, it 

 ought to increase. Perhaps since the difference of latitude 

 between these places is so small, being only 13' 41", the local 

 irregularities and small unavoidable errors of observation may 

 be sufficient to account for this. Indeed it appears to be pre- 

 cisely of such a nature as that which occurred to the late 

 General Mudge in the measurement of an arc of the meri- 

 dian, as well as Capt. Kater at Arbury Hill ; and in either 

 case it would be unfair to impute it totally to errors on the 

 part of the observers or their instruments. 



The compression may now be determined by means of 

 equation (9), thus : 



^_ 5 2 0919576 0-212796 



6 "" ' 2 X 20919576+1856062635x3-250751 39009014' 



e=0'008638-0-005455 = 0-003183= — \- . 



3142 



This compression is somewhat greater than that deter, 

 mined from the experiments of Capt. Kater, which was ■ > 



3*3' 1 



The compression resulting from a comparison of the lengths 

 of the pendulum at the extremities of the arcs, namely, at 



Unst and Formentera, is — -, or a little greater than — — - . 



This also occurred when we examined the experiments of 

 Capt. Kater. 



Two more experiments * have been made which deserve 

 to be examined, namely, that made bv Capt. Sabine at Mel- 

 ville Island in latitude 74° 47' 12"" N., and that at Ma- 

 dras by Mr. Goldingham in latitude 13° 4' 9" N. The 

 length of the pendulum at the former place was ascertained 

 to be 39-207000 inches 



at the latter 39-023380 



from which we obtain 2=39-012710, #=0-208658, 



and e = 0-0086372 -0-0053485 = 0-0032887=^-. 



On considering the results that have been obtained from all 

 these experiments, it appears that the mean compression de- 

 rived from all the experiments in each series of observations, 

 is smaller than that deduced from those made at the extremity 



* The writer of this paper had not got the observations of Capt. Hall, 

 Mr. Foster, &c. at the time it was written. These will form another com- 

 munication. 



of 



