164 Mr J. D. FORBES on the Horary Oscillations 



At Paris, from eleven years' results, the maximum is also in spring, 

 but the principal minimum in summer, and having a second 

 maximum in autumn. On the Plateau of Bogota, near the 

 Equator *, there are two maxima, which appear nearly to coin- 

 cide with the maximum intensity of the solar rays, occurring to- 

 wards the equinoxes. The observations of DORTA, at Rio 

 Janeiro, in 23 S. Lat, give nearly the same results, the maxi- 

 mum being in April, or at the autumnal period in southern 

 latitudes f . It is remarkable also, that the observations of Dr 

 RUSSEL at Berhampour (Lat. 24 N.), and of Mr PRINSEP at 

 Benares (Lat. 25^ N.), each continued for three years, give, 

 severally, a minimum in summer, and one not so low in winter, 

 with a decided maximum in spring, and a strong indication of a 

 smaller one in autumn . If, as I think we have good reason 

 to beh'eve, the real maximum is in spring, according to the majo- 

 rity of observations, we may account for this very general ap- 

 parent maximum in autumn, by considering the effect of change 

 in the hour of tide. For, suppose the barometer observed, as 

 has very generally been the case, constantly at 9 A. M., this cor- 

 responds to the true critical hour very exactly at the equinoxes ; 

 but in summer, as this hour becomes earlier, the barometer will 

 have passed its maximum at 9 A. M., and the oscillation will come 

 out too small, giving an apparent minimum in summer, when 

 perhaps none ought to exist. This, probably, will account satis- 

 factorily for this extensively observed fact, and accords well with 

 the results of my observations at double hours. If we can trust 

 to the reductions of MARQUE VICTOR'S observations at Toulouse, 

 they present the greatest anomaly in this part of the subject. 



* HUMBOLDT, Relation Historique, iii. p. 302 



f Ibid. p. 298. 



| Philosophical Transactions, 1828. 



