Considerations on the Problem of Latitude Variation. 



13 



Ol)<ei'V;itions at Freiburg i. S. made by Hecker at a depth of 

 rJO metixs below the surface of the ground (1910-1911) scarcely 

 showed the solar efïect. It was almost insensible or negligible, the 

 amplitude not exceeding 0. "001. From these facts we can infer 

 that the solar thermal effect is the minore pronounced the shallower 

 the gi\iund work, as might also be guessed from mere conjecture. 



While most horizontal pendulum rooms are deep and are kept 

 in as invariable a temperature as possil)le, our astronomical telescope 

 piers are, on the cont]'ar3% rather shallowly founded and are sul)- 

 jected to the diurnal change of temperature in its full range, from 

 their exposure to the free air. Moreover, astronomical observations 

 are naturally only practicable in clear weather, when the change 

 of temperature of the environment of the pier is great and rapid. 

 Under these circumstances we are led to conclude that the ground 

 and pier, on which the telescope is set up, are undergoing a con- 

 tinuous tilting whilst it is being used in the night, the meridian 

 component of which is in the direction, north downward or south 

 upward, and the magnitude of which is far greater than that experi- 

 enced in the horizontal pendulum observations. There is, however, 

 a contradiction between the European and Japanese observations. 

 In Europe the amplitude is at its maximum in summer and its 

 minimum in winter ; in Japan^\ on the contrary, it is at its maxi- 

 mum in winter and its minimum in summer. This difference may 

 be due to some meteorological causes, depending on the latitude. 

 For low latitudes the latter variation may hold good. It is also 



1) Shida, loc. oit. 



