Royal Society, 147 



arrested, and for the space of about 2000 feet the temperature 

 remains constant or even increases by a small amount : it afterwards 

 resumes its downward course, continuing for the most part to di- 

 minish regularly throughout the remainder of the height observed. 

 There is thus, in the curves representing the progression of tempe- 

 rature with height, an appearance of dislocation, always in the same 

 direction, but varying in amount from 7° to 12°. 



In the first two series, viz. Aug. 17 and 26, this peculiar inter- 

 ruption of the progress of temperature is strikingly coincident with 

 a large and rapid fall in the temperature of the dew-point. The same 

 is exhibited in a less marked manner on Nov. 10. On Oct. 21 a 

 dense cloud existed at a height of about 3000 feet ; the temperature 

 decreased uniformly from the earth up to the lower surface of the 

 cloud, when a slight rise commenced, the rise continuing through 

 the cloud and to about 600 feet above its upper surface, when the 

 regular descending progression was resumed. At a short distance 

 above the cloud the dew-point fell considerably, but the rate of dimi- 

 nution of temperature does not appear to have been affected in this 

 instance in the same manner as in the other series ; the phenomenon 

 so strikingly shown in the other three cases being perhaps modified 

 by the existence of moisture in a condensed or vesicular form. 



It would appear on the whole that about the principal plane of 

 condensation heat is developed in the atmosphere, which has the 

 effect of raising the temperature of the higher air above what it 

 would have been had the rate of decrease continued uniformly from 

 the earth upwards. 



There are several instances of a second or even a third sudden fall 

 in the dew-point, but any corresponding variation in the temperature 

 is not so clearly exhibited, probably owing to the total amount of 

 moisture in the air being, at low temperatures, so very small that 

 even a considerable change in its relative amount would produce but 

 a small thermal effect. 



As the existence of the disturbance in the regular progression of 

 temperature now stated rendered it necessary, in order to arrive at 

 any approximate value of the normal rate of diminution with height, 

 to make abstraction of the portion affected by the disturbing cause, 

 each series was divided into two sections, the first comprising the 

 space below the stratum in which the irregularity existed, and the 

 second commencing from the point where the regular diminution of 

 temperature was resumed. It was then found that the rate of dimi- 

 nution was nearly uniform within each section, but that it was 

 somewhat greater in the lower than in the upper sections. 



On taking a mean of both sections for each series, giving each 

 section a value corresponding to its extent, it is found that the 

 number of feet of height corresponding to a fall of one degree Fahr- 

 enheit is — 



On August 17 292-0 feet. 



August 26 290-7 „ 



October 21 291*4 „ 



November 10 312*0 „ 



L2 



