MfiTEOfcOiOGlCAL JOURNAL FOR 1807,8, 



niohly rises before the observer, and the morning obser- 



vation is registered at too late an hour. To obviate this irt- 



Six's thermo- convenience, I made use of the thermometer invented by 



mended. 00 " 1 " Mr# Six ' wmcn > with a little assistance from the observer, 



gives a correct account of all its variations, by noting edch 



day the two extremes of its range. 



Diumal raria- The diurnal variation of temperature determined by this 



rature mUC " i nstrument > i s certainly more correct than the results of a 



common thermometer. As for the utility of the inquiry, I 



have only to observe, that meteorology is at present in its 



infancy ; and the Cultivators of the science have little to do 



but to collect facts for the use of their successors. 



Tables of the kind here recommended, formed in diffe- 

 rent situations and latitudes, will perhaps prove necessary, 

 when the materials of a rational theory have been collected 

 from long observation. In the mean time we know for a 

 certainty, that the phenomenon in question arises from the 

 sun's arinital motion between the tropics: but the influence 

 of this luminary- is disturbed in the regularity Of its effects 

 by the vicissitudes of the weather ; for the variation is great- 

 est when the atmosphere is clear, and least at the same 

 season when the air is obscured with clouds and rain. These 

 are manifestly causes of irregularity ; but they have not suf- 

 ficient power to prevent the necessary consequences of the 

 sun's motion in the ecliptic, they only retard or accelerate 

 his effects. For supposing the Earth to be destitute of an 

 atmosphere, the sun would produce two maxima and two 

 minima of variation at stated times in the course of a year, 

 according to the doctrine of radiant heat. The minima 

 would coincide with the coldest and hottest days, and the 

 maxima would happen after the two equinoxes, perhaps 

 about the times of mean temperature. These extremes ap- 

 pear in the table, but they are not periodical; which is also 

 the case with the hottest and coldest days, as well as the 

 seasons of mean temperature. 



Rain collected The second subject in meteorology, to which I was de-» 

 at different ele- . ,. j ,, . /»i-,,, 



vations. sirous to attend, was the comparison ot the ram collected 



at different elevations, in the same neighbourhood. For 



this purpose, I made use of two gauges constructed exactly 

 alike ; one of them stood in a garden in the bottom of a 



vallev, 



