Prof. Lloyd on the Magnetic Disturbance of July 2 #4", 184-2. 137 



wrought iron in different stages of its crystallization, as there 

 can be no doubt that very great differences exist in this re- 

 spect, and it is probable that in most cases, when the crystal- 

 lization has once commenced, the continuance of the same 

 causes which first produced it goes on continually increasing 

 it, and thereby further reduces the cohesive strength of the 

 iron. 

 Earl Street, May 31, 1842. 



[Several samples of broken railway axles accompanied this 

 paper, and were exhibited at the Meeting. In some of them 

 the same axle was broken in different places, and showed that 

 where the greatest amount of percussion had been received, 

 the crystallization of the iron was far more extensive than in 

 those parts where the percussion had been less.] 



XXIII. Notice of a remarkable Magnetic Disturbance which 

 occurred on the 2nd and Mh of July, 184-2. By the Rev. 

 Humphrey Lloyd, D.D., F.R.S., V.P.R.I.A., Professor 

 of Natural Philosophy in the University of Dublin. 



To Richard Taylor, Esq. 

 Dear Sir, 



A VERY remarkable magnetic disturbance (the most re- 

 ■^*- mar/cable I ever witnessed) occurred in the beginning of 

 the present month. A brief ske*tch of some of the principal 

 features of the phenomenon, as they were observed at the 

 Dublin Magnetical Observatory, may probably interest some 

 of your readers. 



On the 2nd of July, at 6 a.m. (Gottingen mean time), the 

 attention of one of the assistant observers (Mr. O'Neill) was 

 arrested by the extraordinary deviation of all the magnets from 

 their mean positions, accompanied by a large vibration; and 

 he immediately commenced a series of observations at short 

 intervals. The disturbance of the declination (by which I mean 

 the deviation of the freely suspended horizontal magnet from 

 the mean place corresponding to that horn-) then amounted to 

 149*2 divisions of the scale of the instrument, or 1° 47' # 3 of arc, 

 — the north end of the magnet deviating towards the west, or 

 the declination increased. The magnet of the bifilar magneto- 

 meter was driven beyond the limits of the scale of its colli- 

 mator ; and the diminution of the horizontal intensity exceeded 

 the jpth of the whole force. Both magnets were returning 

 rapidly towards their mean positions at the moment of the 

 first observation ; so that the epoch of the greatest change was 

 before 6 a.m., and its amount exceeded that observed. The 



