XXX 



Introduction to the Makerstoun Observations, 1843. 



Table 10. — Comparisons of the Thermometers with the Bulb free, and with the 



Bulb in a brass bar. 



Gbttingen 



Thermometer. 



Difference. 



Mean Time. 









Ross. 



Adie. 





1844. 









d. h. 



o 







o 



Jan. 2 21 



30-9 



30-7 



0-2 



22 



31-3 



31-0 



03 



23 



31-9 



31-5 



0-4 



Jan. 3 



33-9 



330 



0-9 



1 



38-9 



37-6 



1-3 



2 



42-3 



41-0 



]-3 



3 



44-7 



430 



1-7 



4 



45-6 



44-0 



1-6 



5 



45-9 



44-5 



1-4 



6 



46-0 



44-9 



11 



7 



46-1 



450 



11 



8 



45-9 



44-9 



10 



11 



45-0 



44-3 



0-7 



34. In the adjustment of the instrument, the magnet is forced to a position at 

 right angles to the magnetic meridian, by turning the arms of the torsion circle. 

 As, in forcing the magnet from the meridian, the upper extremities of the wire will 

 move through a greater angle than the lower extremities, the wires will be no longer 

 vertical, and the magnet and appendages will be raised ; the forces producing equi- 

 librium will, therefore, be the weight suspended endeavouring to attain the lowest 

 point, and the horizontal component of the earth's magnetic intensity acting on the 

 free magnetism of the bar, 



35. If f be the excess of the angular motion of the arms of the torsion circle, 

 or upper extremities of the wire, over u, that of the lower extremity or magnetic bar 

 in moving the latter from the meridian, the equation of equilibrium will be 



m X sin u = W-y sin v. 



m, X, W, a, .and I being respectively the magnetic moment of the bar, the hori- 

 zontal component of the earth's magnetic force, the weight suspended, the interval, 

 and the length of the wires. The differential of this equation (u = 90°) divided by 

 it, gives 



A X 



-— — = na cot V + t (Q + 2e — e') 

 X 



n being the number of scale divisions from the zero, or scale reading when if = 90°, 

 a the arc value in parts of radius of one scale division, t the number of degrees 

 Fahrenheit which the temperature of the magnet is above the adopted zero, Q the 



