247 
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 10’.0; and its mean duration is an 
hour and a half. The epoch of the maximum of easterly deflec- 
tion varies from 7} Pp. M., to 14 a.m., the mean epoch being a 
few minutes before 10 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 
mean diurnal curve for the period embraced by the obserya- 
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 larve on which it feeds. This 
is accomplished by snipes, woodcocks, &c., by means of ex- 
