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



we possess at present, it is not to be expected that in English latitudes and 

 under her variable and cloudy skies, the temperature of the solar heat in- 

 cident on the earth's surface, recorded at two stations only, should coincide 

 at all distinctly in variation with that of the heat emitted from the sun. 

 Still, by a very ingenious treatment of the data, Mr. Baxendell succeeded 

 in shewing, with great probability, that the sun's radiation varied in inten- 

 sity directly with the observed number of the spots during the years 1859 

 to 1866. 



It was still desirable, however, that further and more direct proof should 

 be obtained, and it is obvious that for such a purpose, no country offers more 

 favourable conditions than India ; and fortunately, owing in no small degree 

 to the urgent representations of this Society in past years, the means pro- 

 vided by the Government of Bengal, in the establishment of systematic 

 observations throughout its provinces, have put it in my power to bring 

 before the Society this evening, evidence, which if not absolutely conclusive, 

 at least leaves, I think, but little room for doubt, that the old speculations 

 are true ; and that the sun's heat varies from year to year, to such an 

 extent as must appreciably affect terrestrial phenomena. 



Registers of the readings of a maximum thermometer, the bulb of 

 which is coated with lamp-black and which is enclosed in an exhausted 

 tube,* were commenced at a few stations in Bengal in the latter part of 

 1867 or the beginning of 1868 ; at others the observations were begun in 

 subsequent years. The instruments are freely exposed to the sun's rays, 

 supported on forked sticks at a height of one foot above the groundf and 

 their readings have been recorded on all days, whether clear or cloudy. 

 Being very fragile, and exposed without protection, they are unfortunately 

 very subject to breakage, and although therefore their registers extend in 

 most cases over a period of six or seven years, I can find but one station on 

 my list at which the register has been kept continuously for more than five 

 years with one and the same instrument. This fact very much reduces the 

 quantity of data available for discussion. It appears that, from some cause 

 at present unexplained, these thermometers, made by the best London makers, 

 sometimes differ in their readings to the extent of several degrees (I have 

 known differences of 10° and 15°) when exposed under apparently identical 

 circumstances ; and there have been hitherto no means of comparing them 

 together in Calcutta in the only effectual way, viz., by exposing them side 

 by side to the solar radiation, and correcting all to some one instrument, 

 arbitrarily selected as a standard. In dealing with the registers then, I 



* In one of these tubes which I opened, (that of a thermometer by Messrs. 

 Negretti and Zambra,) I found the residual air to have a pressure at the freezing point 

 of 1*26 ins. about equal to a vacuum of £%. 



t At Koorkee the instrument is about 4 feet above the ground. 



