168 Mr J. D. FORBES on the Horary Oscillations 



These observations, then, establish the existence of an oscillation 

 in Lat. 74, nearly equal to that in Lat. 56, and affected by an 

 opposite sign. 



10. The number of observations in different parts of the globe 

 being now very considerable, it appeared to me of high import- 

 ance, in the present state of the science of meteorology, to endea- 

 vour to generalize them, and see how far they might be repre- 

 sented by an empirical law. I was accordingly engaged in classify- 

 ing observations collected from every quarter, when I was fortu- 

 nate enough to meet with an abstract of a very important memoir, 

 by M. BOUVARD, of the observatory of Paris, upon this subject, and 

 read recently at one of the annual meetings of the Helvetic So- 

 ciety. It is upon the hourly variations of the barometer ; and 

 the only abstract of it I have met with is that contained in the 

 Bibliotheque Universelle for 1829, nor have I seen it in any other 

 periodical work. M. BOUVARD, whose important contributions to 

 meteorology are universally known, has here amassed a great 

 addition to the observations collected by HUMBOLDT ; and he 

 undertakes the bold enterprise of representing the extent of the 

 oscillation in any latitude, at any height above the sea, and at any 

 period of the day or year, by an arbitrary formula : but though 

 his table presents perhaps more accordance with observation than 

 might have been expected from so sweeping a generalization, I 

 think there is much reason to question the accuracy of the formula, 

 which is founded on these conditions ; that at the equator the 

 extent of the oscillation is proportional simply to the tempera- 

 ture, on the centigrade scale, of the period during which the 

 oscillation is observed at the given spot, the oscillation and tem- 

 perature at the level of the sea being unity ; that in any other 

 latitude, the same law is to be modified by introducing the addi- 

 tional proportionality to the square of the cosine of the latitude. 

 Or, representing by m and t the tide and mean temperature at 



