Royal Society, 379 



of the pharynx. In Birds it is shown that there is a single mem- 

 branous tube into which the two osseous tubes open ; this mem- 

 branous tube is situated between and is intimately adherent to the 

 inner surface of each pterygoid muscle, and by these muscles the 

 tube is opened. The conclusion to which the author arrives re- 

 specting the influence of the closed Eustachian tubes is, that the 

 function of hearing is best carried on while the tympanum is a closed 

 cavity, and that the analogy usually cited as existing between the 

 ordinary musical instrument, the drum and the tympanum, to the 

 effect, that in each it is requisite for the air within to communicate 

 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. 



Feb. 24. — A paper was read, entitled ** On Periodical Laws in 

 the larger Magnetic Disturbances." By Captain Younghusband, 

 R.A., F.R.S. 



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 (1''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 or 

 disturbance. These were separated into disturbances of the north 



202 



