60 Transactions of the American Institute. 



it is in those tliat are colder. It is always lower, too, in rainy seasons 

 than in dry. Besides these there are annual variations, and these are 

 very small, about a few hundreths of the tenth of an inch, therefore, 

 they are not yet considered within the perfectly well defined varia- 

 tions of the great tides. The others are real tidal waves. I will 

 now speak of the " irregular variations," which are by far the most 

 conspicuous tliat we are acquainted with in this latitude. The baro- 

 meter is falling and rising all the time. Its stationary condition is a 

 very rare thing. If you could have a barometer made of water, a 

 tube filled with water, which should be thirty-three and a half feet 

 long, it would greatly magnify these perturbations, and it would not 

 be seen quiet scarcely for a moment. There would be no such thing 

 as a calm ; its normal condition would be motion. We find this in 

 all barometers in these latitudes, but in the tropics there are scarcely 

 any irregular movements ; hence it is that in those regions you can 

 operate with the barometer with scarcely any corrections ; but the 

 further you go north, the greater the difierences between the extremes. 

 What does this indicate, but the fact that the atmosphere in the extra 

 tropical regions is in constant state of movement and agitation, which 

 causes these immense difierences. The lecturer then went on to explain 

 the causes of these difierences. The rarefaction of the atmosphere 

 by heat causing immense upward movements, succeeded by a down 

 rush of denser air ; the quantities of moisture taken up into the 

 atmosphere ; the diurnal movement of the globe causing modification 

 in the direction of the currents of air, &c. He gave interesting 

 facts in regard to cyclones, the movement of storms, and the uses of 

 telegraphy in averting to some extent the damages by hurricanes. 



The lecture of which we present only a condensed report, was 

 highly interesting, and was listened to throughout with marked 

 attention. 



