Mr. J, Blackwalts Meteorological Observations. [Feb. 

 Results of Two Observations. 



Results of Three Observations.'^ 



The correct extremes for the day, and of course the exact 

 range, are not to be found among these results ; yet the true 

 mean is very nearly approximated in several instances, and in 

 one or two, it may even be considered as obtained with a suffi- 

 cient degree of precision ; but this near conformity to the mean 

 of the 25 observations, is evidently merely accidental; and 

 when it is recollected at what different hours, and with what 

 various instruments meteorologists take their observations, the 

 bad consequences of the present want of system will be very 

 apparent. 



The extremes by the self-registering barometer were 29*610, 

 and 29-190, the mean being 29-400, and the range -420. Here 

 the extremes and range may be looked upon as correct, but the 

 mean is erroneous, exceeding the mean of the 25 observations, 

 by rather more than l-20th of an inch. This arises from the 

 variations of the barometer being irregular between the extremes, 

 a much larger proportion of the observations being below the 

 mean found from these extremes than above it. Whenever the 

 mercury moves uniformly up or down through the natural day, it 

 is plain that the mean found from the extremes must coincide 



* In consequence of a mistake in the Maximum, Minimum, and Range, which was 

 not discovered till too late for correction, they are omitted altogether.— £d. 



