On the Diurnal Motion of the Magnetic Needle. 219 



always felt a strong conviction to the same eflfect ; and, anxious 

 to discover if his investigations had demonstrated the truth of 

 the contested proposition, I devoted my attention to them par- 

 ticularljr^ I hope in a manner consistent with his high position, 

 and with the respect due to extraordinary talent. 



I cannot, however, sacrifice my own convictions to authority ; 

 and I feel bound to declare that, in my opinion, no one has ever 

 yet estabUshed the identity of the agent in all the phaenomena 

 called electric. 



Not having the vanity to suppose that the arguments adduced 

 in this Essay will convert a reader in whose mind the hypothesis 

 of identity is already established, I only venture to hope that he 

 may be induced to reconsider the subject, leaving his judgement 

 free to the reception of new impressions. If I succeed so far, 

 my efforts will be sufficiently rewarded. 



Far from having exhausted my arguments, I may say with 

 Cicero, " hujus autem orationis difficilius est exitum quam prin- 

 cipium, facere : itaque non mihi tam copia quam modus in 

 dicendo quserendus est." 



1 1 Clare Street, Dublin. 



XXXII. On the Decennial Period observed by Dr. Lamont in the 

 Magnitude of the Diurnal Motion of the Magnetic Needle. By 

 P. A. Reslhuber, Director of the Observatory at Krems- 

 miinsier*. 



TOURING the past year I was occupied with the reduction 

 J-' and calculation of the magnetic observations which have 

 been made here since the establishment of the magnetic observa- 

 tory in the year 1839. These observations refer to the absolute 

 determination of the elements of the magnetic force, the daily 

 alteration of the declination and the horizontal intensity, and to 

 the variations of these two elements on the fixed days of obser- 

 vation. 



The observations on the change of the declination and hori- 

 zontal intensity were can-ied out with the magnetometer of Gauss, 

 being performed (\iily since the year 1842 at the hour of 8 o'clock 

 A.M., 2 o'clock P.M., and 8 o'clock p.m. mean Gottingen time; 

 I possess therefore already a series of observations extending over 

 a space of ten years, sufficient to permit some inferences to be 

 drawn from the obtained data. 



With regard, in the first place, to the decennial period disco- 

 vered by Dr. Lamont, the following is the result of our obser- 

 vations : — 



* From Poggendorff'i AnnaUm, vol. Ixixv. p. 412. 



