176 METEOROLOGICAL OBSERVATIONS 
It becomes, therefore, a matter of no small moment, to 
find out, at what hour or hours, the average temperature of 
the day, for the most part, occurs ; that the meteorologist 
may be furnished with accurate information, for the proper 
conducting of his observations, and a long-agitated question 
ifi physical science, finally answered. 
During those ages which immediately followed the in- 
vention of the thermometer, philosophers were guided by 
mere whim and caprice, in settling their hours for observing 
the indications of that instrument. But, since the great 
subject of the mean temperature of the globe has been 
started for discussion, and since the high importance of 
meteorological registrations to the best interests of mankind 
has been generally acknowledged, men of science have all 
agreed in admitting the necessity there is for their observa- 
tions being at least synchronous one with the other. This 
is, however, not sufficient for the purposes of philosophy. 
If the mean temperature of the day is not ascertained by 
all, the synchronism of the observations matters but little. 
Many different hours have been proposed as the best suited 
for the attainment of the object desired, but perhaps too fre- 
quently on unstable grounds. After the maximum and mi- 
nimum thermometers had deservedly come into general use, 
the hours of 10 a. m. and 10 p. m. were confidently stated 
as the preferable ones for observation ; the mean of these 
agreeing with the mean of the extremes indicated by the 
instruments alluded to ; that, again, being supposed by 
many, palpably to demonstrate the true average temperature 
of the twenty-four hours. 
The only mode, however, that can be adopted, defini- 
tively to settle the disputed point, plainly is, to make a 
continued series of observations for a considerable period of 
time, at the lapse of very short intervals, — as for two or 
three years, at the end of every half hour, day and night, — * 
