34 H F. Blanford — On some recent Evidence of the [No. 1, 



and adopts the earlier hypothesis of De la Lande and of Zollner that they are 

 solidified scoriaceous masses floating on the glowing fluid surface [" Schollen 

 fest-gewordener Stoffe auf der gluhendflussigen Sonnenkugel"]. The great 

 discovery of Chacornac and Lockyer in 1865, that the spots are produced by 

 a down-rush of the cooled external atmosphere of the sun, would seem to be 

 unknown to him. 



The spots being then, in all probability, an indication of increased ra- 

 diation, how is this to be reconciled with the facts ascertained by Professor 

 Koppen. Possibly, I think, in this way. The temperatures dealt with by 

 Professor Koppen are of course those of the lowest stratum of the atmo- 

 sphere at land stations ; and must be determined, not by the quantity of heat 

 that falls on the exterior of the planet, but on that which penetrates to the 

 earth's surface, chiefly to the land surface of the globe. The greater part 

 of the earth's surface being, however, one of water, the principal immediate 

 effect of the increased heat must be to increase the evaporation, and there- 

 fore, as a subsequent process, the cloud and the rainfall. Now a cloudy 

 atmosphere intercepts the greater part of the solar heat ; and the re-evapora- 

 tion of the fallen rain lowers the temperature of the surface from which it 

 evaporates and that of the stratum of the air in contact with it. The heat 

 liberated by cloud condensation doubtless raises the temperature of the air 

 at the altitude of the cloudy stratum ; but, at the same time, we have two 

 causes at work, equally tending to depress that of the lowest stratum. A.s 

 a consequence, an increased formation of vapour, and therefore of rain, fol- 

 lowing on an increase of radiation, might be expected to coincide with a 

 low air-temperature on the surface of the land. 



It is needless to point out that a vast train of enquiry is opened up by 

 the fact, once established, that the solar heat undergoes a periodical varia- 

 tion. It is I believe of high importance to Meteorology, or will be so when the 

 amount of the variation shall have been ascertained in terms of absolute mea- 

 surement, and it affords a strong additional incentive to the establishment 

 of an observatory in India, such as have already been founded under the 

 less favoured skies of Germany and on the Rocky mountains, for observing 

 and measuring the variations of the sun. These and their immediate effects 

 are, by prerogative, the study of the tropics. 



P. S. July 12th. — Since the foregoing paper was read, I have examined 

 the register of Darjiling ; a station which, although frequently obscured by 

 cloud, has the advantage over stations on the plains, that it is above the 

 level of the dust haze that absorbs so much of the solar heat over the latter. 

 I have discussed the registers by a method somewhat different from either 

 of those followed in the body of the paper, viz., by selecting the three high- 

 est recorded sun temperatures in each half month, deducting from each the 

 maximum temperature of the air in the shade on the same days, and taking 



