552 Account (^Meteorological Observations made in 
5. Experiments for ascertaining which three Hours of the Day 
give a Mean nearest the True Mean Temperature. 
Professor Dewey undertook a series of observations in the 
years 1816 and 1817, in order to ascertain the three times 
of the day when observations should be made with the thermo- 
meter, in order to obtain a mean nearest to the true mean tem- 
perature. In order to do this, he observed the thermometer 
twenty-four times each day, or once every hour, during thirty 
days, at different times of the year, and he obtained the follow- 
ing results : 
Mean of 24 observations during each hour of 30 days, * 41®.50 
of 7** A. M. and 2^ A. M. - - - - 42.47 
of highest and lowest, - - - - . 42.66 
— — do. do. means, 42.69 
about sunrise and sunset, - - » - 40.88 
of 8h A. M. Ih P. M. and 6i» P. M. • - . 45.00 
Hence Professor Dewey concludes that 7^ A. M., 2^ P. M. and 
9^ P. M. are the best three hours of observation. 
With the interesting data furnished by Professor Dewey, we 
were naturally anxious to ascertain whether or not the hours of 
10^ A. M. and 10^ P. M., as recommended by the Meteorolo- 
gical Committee of the Royal Society of Edinburgh, and first 
employed and suggested by the Reverend Robert Gordon, as 
an approximate result to the mean of the highest and lowest 
diiring the day, were such as to 
The following are the mean of the five series of observations 
made by Professor Dewey : 
Mean of lO** A. M. Mean of 24 £)bservations, 
and 10*^ P. M. or one every hour. 
1816, March 23.-29. - 37°.67 39°.05 < 
April 1.-5. . 41.48 41.76 
July 23 — 27. - 63.46 47.69 
October 28.— Nov, 1. 48.55 64.35 
1817, Jan. 6.— Feb. 6. - 16.10 14.66 
Mean of 2 Observations at 10** Mean of 24 Ob- 
A. M. and 10** P. M. 4r,45 servations, 41®.50 
This result must be considered as a very extraordinary one, 
as the mean of 10^^ A. M. and 10^ P. M. is within of a 
* Hours proposed by the Philosophical Society of New York. 
