140 Prof. Lloyd on the Magnetic Disturbance of July 2 Sf^ 1842. 



with the other two instruments ; but the observations are un- 

 reduced, and I am therefore unprepared as yet to offer any 

 remark respecting the changes of inclination or total intensity. 

 It is manifest, however, even from this imperfect sketch, that 

 this disturbance presents many features of prominent interest: 



1. In the great magnitude, and marked and abrupt cha- 

 racter of the principal changes. In both these respects the 

 changes at 6 a.m. and 12 p.m. on the 2nd instant, afford per- 

 haps the most interesting points of comparison of any that the 

 system of simultaneous observation has yet furnished ; and 

 much light may be expected to be thrown on the phaenomena 

 by a comparison of the results which may certainly be ex- 

 pected to arrive from the colonial observatories, as well as of 

 those which have been probably obtained at Port Louis, in 

 the moveable observations of the Antarctic expedition. 



2. In the striking confirmation which it affords to the con- 

 clusion of Prof. Kreil, viz. that all the greater changes are 

 accompanied by a diminution in the horizontal component of 

 the intensity. The whole of the day following the disturbance 

 (July 5) was also characterized by a diminished intensity, 

 which is also in accordance with the inductions of Prof. Kreil; 

 but the increase of this element towards the close of the dis- 

 turbance (in the afternoon of the 4th) is in opposition to one 

 of his conclusions. 



3. In the two classes of changes exhibited; in one of which 

 (as on the evening of the 2nd) the disturbances from the mean 

 position, although great and rapid, were accomplished with- 

 out any sensible vibration of the magnets ; while in the other 

 (as on the morning of the 4th) the vibration exceeded any 

 ever witnessed in this observatory, since the application of 

 the copper rings. 



4. In the occurrence of great magnetic changes without 

 any marked auroral phaenomena. The sky was clear on the 

 night of the 2nd, during a very remarkable part of the dis- 

 turbance, and a light was seen in the N.W., — but of a very 

 uncertain nature, and without any of the distinguishing cha- 

 racters of the aurora. I may observe, however, that through- 

 out the whole of the 3rd, and the greater part of the 4th, the 

 sky was covered during the day with a peculiar milky white- 

 ness, apparently belonging to something distinct from and 

 above the clouds ; and that this disappeared suddenly, and 

 the blue sky became visible, about 5 p.m. on the 4th, when 

 the disturbance was at an end. I could not help regarding this 

 appearance as connected with aurora. 



Believe me, dear Sir, faithfully yours, 

 Trinity College, Dublin, H. Lloyd. 



July 19, 1842. 



