70 H. F. Bl an ford — On the relations of cloud [No. 2, 



J. Allan Broun, F. R. S. contributed to " Nature" shortly before his decease, 

 and in which he endeavoured to show, that while air must unquestionably 

 expand and contract according as its temperature rises and falls, the varia- 

 tion in density so produced in no way adequately accounts for the annual 

 variation of monthly mean barometric pressure at the surface of the earth. 

 Mr. Archibald, following a method which I proposed in a paper in the 

 Phil. Trans, in 1874, computes the variations of density, which the at- 

 mospheric column below Darjiling undergoes month by month, in conse- 

 quence of the variations of temperature, humidity and top-pressure ; and 

 shows that the lower stratum of the atmosphere, thus subjected to a 

 physical analysis, conforms in its changes, with near approximation, to the 

 indications of theory ; and that, of the several causes affecting its density 

 and static pressure, temperature is by far the most influential. This con- 

 clusion is also that at which I arrived in the paper above referred to, work- 

 ing on far more restricted data than those discussed by Mr. Archibald, but 

 the best then available to me. 



Mr. Archibald has taken as the subject matter of his paper, the nor- 

 mal or average values of pressure, temperature &c, as given by many years' 

 registers at Darjiling and Goalpara. In the latter part of the present paper, 

 I have compared the abnormal variations of temperature with those of the 

 density of the atmospheric column, below the three hill stations Chakrata, 

 Ranikhet and Pachmarhi, and have shown that, in their case also, tem- 

 perature and density vary inversely, in accordance therefore with the 

 results previously obtained by myself and Mr. Archibald, and in accordance 

 also with the indications of theory. 



It seems, therefore, to be fairly established that, as regards the lower 

 stratum of the atmosphere, the anomaly pointed out by the late Mr. Broun 

 does not exist. Observation and theory are here as consistent as the char- 

 acter of the data would lead us to anticipate ; and we must therefore look 

 to the condition of the higher strata of the atmosphere, those which lie above 

 the level of our Indian hill stations, Darjiling, Chakrata &c, for the expla- 

 nation of the apparent inconsistency to which Mr. Broun drew attention. 

 In connection with this enquiry, the facts brought forward in the present 

 extracts from my report seem to me to have much significance. 



I may mention that the whole of this was written and in type (for the 

 Report) before I had seen Mr. Archibald's paper above referred to. 



Some other general questions of importance are referred to incidentally 

 in the course of discussion, in the extracted passages. 



On the mean of all Indian stations, the temperature of the year 1879 

 was slightly below the average, but it was by no means generally so in 

 Northern India. In the North- West Provinces and Bengal, the mean 



