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LXXXVI. Summary of Meteorological Observations made at 

 Paris during the Year 1816*. 



1 HE thermometer which is kept at the Royal Observatory is 

 exposed to the north, at about eight metres (24 feet) above the 

 ground, and in a wooden case around which the air circulates 

 freely. The graduation has been verified by that of an excellent 

 instrument constructed by M. Gay Lussac himself, with all the 

 precaution necessary to secure the utmost exactness. The de- 

 grees have in all our tables been reduced to those of the centi- 

 grade scale. 



It appears to result from the recent researches of M. Hum- 

 boldt, that in all climates we may, without the risk of any sen- 

 sible error, take as the mean temperature of every day, the mean 

 of the extreme temperatures. The minimum being observed at 

 •sunrise, the maximum about three o'clock P.M., the half of the 

 sum of the indications of the thermometer at these two periods, 

 for all the days of each month, will furnish the numbers which 

 express the mean temperatures of the twelve months of the year. 

 In the table which follows, we have placed the results of 1815 by 

 the side of those of 1816. It will be seen from these, that ill 

 regard of temperature, these two years differ much less than we 

 might have been led to suppose. The extremes of the thermo- 

 me'ter in 1816 have been : + 28'^ July20th, and — 1°,8 Feb.l 1th. 



Ternperature of the Vaults of the Olservatonj. 



The observation of the thermometer, in subterranean situ- 

 ations, has acquired great interest, since geometricians have de- 

 monstrated, that at a sufficient depth the temperature, under 

 every latitude, ought, abstracting accidental causes, to be the 

 mean of the temperatures of the surface. A glance at the fol- 

 lowing table will show, that at 28 metres (85 feet) under the 

 ground (which is precisely the depth of the vaults of the Obser- 

 vatory) the diuinal and even the annual variations of the ther- 

 mometer are altogether imperceptible. 



At Paris, the mean of the temperatures of the surface does 

 not appear to surpass 10^ 6', that of tlie vaults is 12° 1' : it is 

 difiicult to assign the cause of so great a difference. 



Hi/grometer. 



Our hvgrometer has been constructed by Richer : it is placed 

 in the shade, and towards the north. In the subjoined table we 

 have onlv noted the observations made at three o'clock P. M., 

 which, making allowance for accidental circumstances, is every 

 ^uv the period of the greatest dryness. On referring to the 



* From the Annates de C/iimie for Dec. 1816. 



separate 



