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mental to insure, if not a conclusive result, at least a satisfactory procedure.
Thus, the thermometers for showing the intensity and calorific effects of solar rays were observed simultaneously with the motion of the sun, when its declination allowed the altitudes to be ascertained in an artificial horizon: when this could not be done, time, latitude, and longitude were noted, and the altitudes computed by Raper's formulae.
In the comparison of the different elements thus secured in New South Wales, with those secured in Van Diemen's Land, such of the series only have been compared together in which the meridional altitude of the sun has corresponded most nearly: and this indispensable condition, with others, also of paramount importance, such as a clear sky and the absence of wind, has rendered the accumulation of good observations so difficult a task, that out of 120 registered series, only fourteen have been found fit to be compared together and laid before the reader.
They are arranged in seven tabular comparisons, beginning with the series possessing the highest meridional altitude, and closing with those which possess the lowest.
The first column of each table refers to civil time, and that, as will be seen, differs in the compared localities: the difference in days and months was the necessary consequence of its being requisite to obtain equal meridional altitudes of the two localities: the difference in years resulted from various demands on my time to which having other observations to attend I was obliged to submit.
The distance of one station from the other, according to the second column in the four first tables, is equal to 8° 35' 25" latitude, and 4° 49' 5" longitude. The difference in height above the level of the sea is trifling; that of the station in Van Diemen's Land being fifteen feet, and that of the one in New South Wales being ten.
In the three last tables, the localities at which observations were taken in New South Wales is shifted farther south, and also more to the westward: hence the distance between the two stations is reduced to 6° T 55" of latitude, and 0° 49' 5" of longitude. The difference in the relative height was, however, thus increased; Ellerslie being 1246 feet above Launceston.
The column of the sun's declination shows that such declination is S., and that throughout the instituted comparisons it decreases: its hourly change was noted for the better appreciation of the element which follows: —