2 John Eliot — On the occasional Inversion of the Temperature [No. 1, 



facts and causes of these occasional inversions of temperature in North- 

 ern India. 



Before commencing with the subject proper of the paper it is de- 

 sirable to give a summary of v\rhat is known generally of these occasional 

 inversions of the ordinary vertical temperature relations. 



Ferrel states it is probable the diurnal temperature oscillations of 

 the upper strata of the atmosphere in the open air away from the in- 

 fluence of contact with the Earth's surface are extremely small. The 

 effect of the Earth's temperature on that of the air above is not so 

 great as it is below, so that this causes the amplitudes in the oscilla- 

 tions of the air temperature near the Earth's surface, though less than 

 those of the Earth's surface, to be greater than those of the air 

 above. The effect of this, it is readily seen, is to cause the temperatures 

 in winter and during the night to approximate more nearly to the tem- 

 peratures above, and hence to diminish the rate of decrease of tempera- 

 ture with increase of altitude at these times. But during the summer 

 and the warmest part of the day, the effect is the reverse ; it causes the 

 temperatures below to differ still more from the temperatures above, and 

 hence to increase the rate of diminution of temperature with increase of 

 altitude. In the diurnal oscillations the rate near the surface at night 

 from the effect of nocturnal cooling is reversed for some distance above the 

 Earth's surface, the temperature being greater above than at the surface. 

 As the Earth cools, the air in contact also cools when the air is calm ^ 

 until the surface and likewise the lower air strata are cooled very low 

 and the law of decrease of temperature is reversed. It is different 

 during the day. The increase of the temperature of the Earth's surface, 

 and of the lower strata in contact, brings about a state of unstable equi- 

 librium from which at once arises a vertical interchange of air, by means of 

 ascending and descending currents, which tend to equalize, in some mea- 

 sure, the temperatures above and below, so that, although the Earth's sur- 

 face may be heated to a much higher temperature than the air immediately 

 above, the decrease of temperature with increase of altitude never becomes 

 very much greater than that of about 1° C. for 100 meters, corresponding 

 to the initial state of unstable equilibrium. The effect of the heat of the 

 Earth's surface cannot be confined to the lower strata merely, as that of 

 the cooling of the surface is, but, as soon as the first stratum in contact 

 with the Earth is heated, the effect is carried to those above. 



Spriing also refers in his meteorology to the same subject and states that 

 the inversion of the ordinary temperature relations takes place occasionally, 

 and usually during periods of very high pressure, and when the amount 

 of cloud and humidity is abnormally small. The cause of the increased 

 temperature at a higher elevation is ascribed to compression of the air. 



