24T 



of testing this hypothesis, and of distinguishing the two classes 

 of disturbances, if they really co-exist. The inspection of 

 these observations has nearly satisfied him of the truth of this 

 view ; and he believes that it will be found, upon a more minute 

 examination, that there are two classes of disturbances, one 

 periodical and local, the other irregular and universal. Of 

 the former, the principal (if not the only one) is that which 

 occurs about 10 p. m., and which causes the north pole of the 

 magnet to deviate to the east. The magnitude of this dis- 

 turbance is on the average lO'.O ; and its mean duration is an 

 hour and a half. The epoch of the maximum of easterly deflec- 

 tion varies from 7 J p. m., to 1^ a. m., the mean epoch being a 

 few minutes before lO p.m. ; and, hence, it is evident, that its 

 effect on the monthly mean curve is to produce a general in- 

 crease of the negative ordinate between these limits of time, 

 as well as the minimum which occurs at 10 p.m. 



It seems to follow also, from these facts, that the ordinary 

 mode of grouping the observations, by taking the mean of all 

 the results at the same hour, — although it truly gives the 

 mea7i diurnal curve for the period embraced by the observa- 

 tions, — does not represent the actual course of the movement 

 during any one day. In order to obtain the representative, 

 or type curve, as it may be called, it seems necessary to com- 

 bine the results in a different manner, of which the author 

 hopes to speak more fully upon a future occasion. 



Mr. Ball exhibited a specimen of Apteryx Australis, recently 

 purchased for the University Museum, and made some obser- 

 vations on the species, referring to the elaborate papers of 

 Yarrell and Owen in the Transactions of the Zoological So- 

 ciety of London. He noticed the adaptation of the position 

 of the nostrils of the bird to its wants; being placed at the 

 end of the bill, it is enabled, by its powerful olfactory appa- 

 ratus, to detect the burrowing larvfe on which it feeds. This 

 is accomplished by snipes, woodcocks, &c., by means of ex- 



