346 AZIMUTHAL CHANGES OF HILLS. 



I now feel myself justified in calling geological with thermal 

 changes, T proceeded to examine the temperature results at the 

 Royal Observatory of Greenwich. For this purpose I examined 

 the readings : 



1st, of Thermometers in the external atmosphere. 

 2nd, of those at a depth one inch below the surface. 

 3rd, ditto ditto 3'2 feet ditto ditto 

 4th, ditto ditto 6 ditto ditto ditto 

 5th, ditto ditto 12 ditto ditto ditto 

 6th, ditto ditto 26 ditto ditto ditto 

 Out of all these classes of observations none appeared to accord 

 so well with the azimuthal changes as those made with 

 thermometers whose bulbs were placed twelve feet below the 

 surface of the ground. In this case the minimum temperature 

 corresponded to about the end of March, and the maximum 

 temperature to about the middle of September. 



I do not at the present time pretend to offer any theory upon 

 this intereresting subject, I merely state facts as I find them, 

 with the full conviction that they will be found useful in future 

 investigations. 



Since the preparation of this paper I have found, what I was 

 not previously aware of, that this subject had been, to a certain 

 extent noticed by Mr. Ellis of the Greenwich Observatory, in the 

 year 1859. His investigations are conducted somewhat differ- 

 ently from mine, and he devotes himself more to the periodic 

 changes of level than of azimuth, and endeavours to combine 

 the two elements. Whilst, however Mr. Ellis's results are more 

 general than mine, yet they do not exhibit those very decided laws 

 which I have endeavoured to establish, but it is satisfactory to 

 find that his conclusions all tend to the same point. And it is 

 singular that quite unintentionally I have commenced my investi- 

 gations at the very point where he left off. Mr. Ellis examines 

 the years 1850 to 1857 included, and I have confined myself to 

 the four succeeding years, and this may perhaps account for the 

 greater regularity observable in my results the instrument and 

 piers having had time to assume what may almost be called a 

 permanent position. 



