136 Baron Humboldt on the Mean Temperature 



to raise the vertical piston would be considerable when the ex- 

 haustion of the receiver was carried to a great length. To 

 obviate this inconvenience, the horizontal piston rod might be 

 made to work in air-tight leather collars at the top of the two 

 horizontal cylinders, while the air coming from the receiver, 

 on each stroke of the descending piston, would pass off by a 

 discharging valve in the same situation. This construction is 

 represented by Fig. 14. The valves require to be permanently 

 raised when the instrument is used as a condenser. Your 

 most obedient Servant, 



Andrew Buchanan. 

 40, George's Square, Glasgow. 



Art. XIX. — Observations on the Mean Temperature of 

 the Equatorial Regions. By Baron Alexander Hum- 

 boldt. 



In an interesting memoir on the temperature of the different 

 parts of the torrid zone at the level of the sea, just published 

 by Baron Humboldt in the Annates de Chimie, fyc. for Sep- 

 tember last, he has entered into an examination of the equa- 

 torial temperature, in reply to the observations of Mr Atkin- 

 son, to which we have already referred in a former article.- 

 The importance of this part of his paper is such as to merit 

 the particular attention of our meteorological readers. 



"The question," says he, "of the equatorial temperature has 

 been recently discussed in a memoir published by Mr Atkinson, 

 in the second volume of the Memoirs of the Astronomical Socie- 

 ty of London (p. 137-183,) and which contains very judicious 

 considerations on several important points of meteorology. The 

 learned author endeavours to deduce from my own observations, 

 by employing the artifices of the most rigorous calculus, that the 

 mean temperature of the equator is not less than 84°.5 Fahr. 

 and not 81°.5, as I have supposed in my essay on isothermal 

 lines. Kirwan made it 84°, and Dr Brewster in his Climateric 

 Formulae has adopted 82°.8. * (Edinburgh Journal of Sci- 

 ence, 1825, No. vii. p. 180.) 



• We have adopted 82°.8 as the equatorial temperature in the warm 

 meridian passing through Africa; but have retained 81°.5, Humboldt's 



