1864.] 



Magnetograph'traces at Kew and Lisbon, 



111 



of equations of the form ax'^-\-ax"^-{-a"x"'^=0 (Legendre, Theorie des 

 Nombres, vol. i. p. 47; Gauss, Disq. Arith. arts. 294, 295, & 298). It is 

 equally applicable whether the coefficients and indeterminates of / are real 

 integers, or complex integers of the ty^Q p-\-qi. 



It will be observed that if /, /".,. are forms contained in the same 

 genus, the equations/=0,/'=0,/"=0, &c. are either all resoluble or all 

 irresoluble. 



IV. "Results of a Comparison of certain traces produced simulta- 

 neously by the Self-recording Magnetographs at Kew and at 

 Lisbon ; especially of those which record the Magnetic Disturb- 

 ance of July 15, 1863.^' By Senhor Capello, of the Lisbon 

 Observatory, and Balfour Stev^^art, M.A., F.E.S. Received 

 January 14, 1864. 



The National Portuguese Observatory established at Lisbon in connexion 

 with the Polytechnic School, and under the direction of Senhor da Silveira, 

 has not been slow to recognize the advantage to magnetical science to be 

 derived from the acquisition of self-recording magnetographs. Accordingly 

 that institution being well supported by the Portuguese Government, de- 

 spatched Senhor Capello, their principal observer(one of the writers of this 

 communication), with instructions to procure in Great Britain a set of self- 

 recording magnetographs after the pattern of those in use at the Kew Ob- 

 servatory of the British Association. 



These instruments were made by Adie of London, and when completed 

 were sent to Kew for inspection and verification, and Senhor Capello resided 

 there for some time in order to become acquainted with the photographic 

 processes. The instruments were then taken to Lisbon, where they arrived 

 about the beginning of last year, and they were forthwith mounted at the 

 Observatory, and were in regular operation by the beginning of July last. 



It had been agreed by the writers of this paper that the simultaneous 

 magnetic records of the two observatories at Kew and Lisbon should occa- 

 sionally be compared together, and the opportunity for such a comparison 

 soon presented itself in an interesting disturbance which commenced on the 

 15th of July last. The curves were accordingly compared together, and 

 the results are embodied in the present communication. 



We shall in the first place compare the Kew curves by themselves, se- 

 condly the Lisbon curves in the same manner, and lastly the curves of the 

 two Observatories together. 



Comparison of Kew Curves, 



The disturbance, as shown by the Kew curves, commenced on July 15th, 

 at 9'' IS'^^'O G.M.T., at which moment the horizontal-force curve recorded 

 an abrupt augmentation of force. The vertical component of the earth's 

 magnetic force was simultaneously augmented, but to a smaller extent ; 

 while only a very small movement was visible in the declination curve. 



