WCP4980

[1]¹ [p. 336]

Waldron Edge, Duppas Hill, Croydon,

11^th October 1879.

James Croll, Esq.

My dear Sir,—I know so little of meteorology that I should prefer not to write to Nature on the subject. If you or Mr. Buchan would do so, it would, I am sure, receive more attention.

I should think Quito would be the best place for such observations, as I fancy the atmosphere is pretty [2] [p. 337] clear all the year round, and there must be some European residents who could make such observations if instructed.

But could not valuable results be obtained at some of our regular meteorological observatories, such as Bombay, by taking a series of black bulb observations in July and January at equal altitudes of the sun, and with equal transparency of the air. The latter factor might, I should think, be determined sufficiently by observing the colour of the sky, as uncondensed vapour is, I believe, quite diathermous to direct rays. Of course, to make the observations comparable, the temperature of the air should also be equal, but a correction for this might probably be arrived at.

Am I not right in supposing that observations made at any latitude in July and January, with the same altitude of the sun, the same transparency of atmosphere, and the same temperature of air, ought to give the results we require, and though the extreme differences of air temperature in our latitude in July and January might prevent any good results being obtained, that would not be the case within the tropics.

Neither at Bombay nor at Batavia, where there are regular meteorological observatories, do they seem to make a single observation of direct sun heat. Mr. Buchan would be the proper person to call attention to this, and to show the interesting physical problems which a series of such observations would help to solve.—Believe me, yours very faithfully,

Alfred R. Wallace.