108 Captain Newbold on the Temperature of 



height from the sea level is in strict accordance with this rule. 

 The mean of a month's observations by Lieut. Campbell, at the 

 summit and base of the rock of Raya-Cottah, on the tableland of 

 Mysore, above which it is elevated 500 feet, gave a decrease of 

 temperature amounting to 3"*35. The diurnal mean difference be- 

 tween the temperature of the summit of a mountain on the table- 

 land of Bellary, and that of the plain at its base, I found so great as 

 7°'5 for the 1500 feet of elevation which separates them. This 

 table land has a mean temperature of nearly 4°"5 above its calcu- 

 lated mean. The difference of temperature of two wells, one at the 

 summit of Mount Sinai, and the other 2000 feet below, amounted 

 to 6°, a result closely approximating that of the comparative obser- 

 vations at Geneva and St Bernard. 



The highest known mean temperature of any place in India is 

 that of Pondicherry, which, though this city stands only a little 

 more than a degree to the south of Madras, is stated to reach 

 85°-28. That of Madras, in lat. 13° 5'N., is 80°-42, and of Colum- 

 bo, more than 5° nearer the equator than Pondicherry, only 80°*75. 

 I am not aware that any reason has been assigned for this extraor- 

 dinarily high mean temperature; the lower temperature of some 

 wells in the vicinity of Pondicherry leads me to doubt its correct- 

 ness. 



BoussingauWs Mode of Ascertaining the Mean Temperature of 

 Tropical Countries. — ■ An expeditious mode for ascertaining the 

 approximate mean temperature of equinoctial regions has been 

 proposed by M. Boussingault, and recommended to travellers, on 

 occasions where time and opportunity do not admit of the usual 

 means. I hardly need remark, that this method is grounded on the 

 hypothesis that, between the tropics the temperature of the earth^s 

 crust is constant at the depth of about a foot (one-third of a metre) 

 beneath its surface, and consists in smking a thermometer in the 

 soil perforated to this depth, under sheds, huts of natives, or other 

 spots sheltered from direct warmth produced by absorption of the 

 solar heat, from nocturnal radiation, and from infiltration of rain 

 water. The result of my own experiments in India indicates that the 

 soil, at the depth of a foot, is subject to an annual, and, in light 

 soils, to a diurnal fluctuation, varying according to the intensity of 

 the sun's rays on the soil surrounding the sheltered spots where the 

 experiments were conducted, and radiation modified by the dry and 

 open, moist and close nature of the soil. During cloudy weather 

 these fluctuations were consequently found at their minimum. The 

 maximum of diurnal fluctuation observed was at Bellarey, on the 

 centre of the tableland of peninsular India, in lat. 15°* 5 N. and 

 1600 feet above the sea level ; mean temperature about 80°'5, 

 The experiments were made in the hot month of May, sky un- 

 clouded ; the soil was reddish, and light in texture, and completely 



