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freely with the outer air, is not correct. On the contrary, the author 

 shows that no displacement of the air is requisite for the propagation 

 of sonorous undulations, and that were the Eustachian tubes con- 

 stantly open, these undulations would extend into the cavity of the 

 fauces, there to be absorbed by the thick and soft mucous membrane, 

 instead of being confined to the tympanic cavity, the walls of which 

 are so peculiarly well adapted to the production of resonance, in order 

 that they shall be concentrated upon the labyrinth. 



In corroboration of the above views the author states, that in 

 cases of deafness dependent simply upon an aperture in the mem- 

 brana tympani, whereby the sonorous undulations are permitted to 

 escape into the external meatus, the power of hearing has been 

 greatly improved by the use of an artificial membrana tympani 

 made of vulcanized india-rubber or gutta-percha, which is so applied 

 as again to render the tympanum a closed cavity. 



February 24, 1853. 

 COLONEL SABINE, R.A., Treas. & V.P., in the Chair. 



A paper was read, entitled " On Periodical Laws in the larger 

 Magnetic Disturbances." By Captain Younghusband, R.A., F.R.S. 

 Received February 16, 1853. 



In this communication the author has arranged, in tables, the 

 disturbances of the magnetic declination at St. Helena and the Cape 

 , of Good Hope, for the purpose of exhibiting the systematic laws by- 

 which those phenomena are regulated, which were long described 

 as irregular variations, because they were of occasional and appa- 

 rently uncertain occurrence. 



The frequency of the disturbances, and their amount, whether 

 viewed separately as easterly or westerly movements, or as general 

 abnormal variations (easterly and westerly being taken together), is 

 shown to be dependent upon the hour of the day, the period of the 

 year, and upon the year of observation. This dependence upon the 

 year of observation affords additional testimony of a periodical varia- 

 tion in the magnitude of magnetic changes of the same character as 

 that which has been found to exist at other places, and which has 

 been considered to be coincident with variations of the solar spots. 



The disturbances of larger amount only are noticed ; those ob- 

 servations which differed by 2'5 scale divisions (l'*8 in arc at St. 

 Helena, and 1''9 in arc at the Cape) and upwards, from the normal 

 place, were separated from the others and the values of the differ- 

 ences taken ; there were therefore two series of figures to be dealt 

 with, viz. the number of disturbances, and the aggregate amount of 

 disturbance. These were separated into disturbances of the north 

 end of the magnet towards the east and towards the west, and the 

 effect of each considered separately. 



The periodical character of disturbances at St. Helena and the 

 Cape in a cycle of years is indicated insofar as the limited extent of the 

 observations would permit ; sufficient however to point to the year 



20* 



