Mr. C. Brooke on a remarkable Magnetic Disturbance. 35 



The preceding table shows that there are indeed a great 

 number of substances still to be discovered. In the first series 

 it will be seen that as yet we have only one member, semi- 

 naphthalidine*,the base correspondingto aniline and toluidine, 

 and obtained by Zinin in a very curious reaction of sulphide 

 of ammonium on dinitronaphthalol. The second series is best 

 known ; it is closely connected with the indigo series by sali- 

 cylic acid, nitrosalicylic acid and aniline. As however the 

 term of indigo is as 'yet not represented in any of the other 

 families I have omitted to connect them. The third is the 

 toluyle series, which has become enriched by the present in- 

 vestigation with two of the principal terms : of the following 

 no term whatever is known. The next contains a series of 

 interesting compounds arising from oil of cumin, and of the 

 last group we have at present only cymol. In a future paper 

 I hope to introduce some of the substances deriving from 

 this carbo-hydrogen. 



This investigation was conducted in the laboratory of the 

 Royal College of Chemistry, and I cannot bring it to a con- 

 clusion w^ithout acknowledging the great obligation I am 

 under to Professor Hofmann for the constant advice and assist- 

 ance which he afforded me during its prosecution, and ex- 

 pressing my warmest thanks to him for his valuable instruc- 

 tions in the method of conducting organic investigations 

 generally. 



IV. An Account of the remarkable Magnetic Disturbance -which 

 continued from the 22nd to the 25th of October i8i7. By 

 C. Brooke, M.B., F.R.S.f 



[With a Plate.] 



DURING this period, which was marked by the appear- 

 ance of the unusually splendid Aurora Borealis described 

 in the November Number of this Joinnal, a greater amount of 

 consecutive disturbance of the magnetic instruments took place 

 at the Royal Observatory than has ever been noticed since 

 the establishment of the magnetic department. 



A continuous record of the great and incessant changes of 

 declination and horizontal force has been obtained by the self- 

 registering photographic apparatus designed by the writer, 

 and described in the Philosophical Transactions, part 1, 1847. 

 The vertical element of magnetic force was not subjected to 

 any corresponding amount of variation. By permission of the 

 Astronomer Royal, a fac-simile of one of the most remarkable 

 portions of the register of the declination magnet is annexed, 



• F.vdmann's .loiivnal, xxxiii. 29. 

 t Comniunicated by the Author. 

 D2 



