..! MR. W. H. DINES ON THE VERTICAL TEMPERATURE 



thi-re is a definite height at which the temperature gradient becomes zero, or is 

 reversed in sign, and with a very few exceptions this definite height lies between 7 '5 

 and 12'5 km. In three cases out of four the lowest temperature met with occurs at 

 this jx>int. No appropriate and convenient name has been as yet assigned to it ; 

 following Messrs. GOLD and HAKWOOD, its height will be denoted by H, and the 

 temperature at the same point by T,.. There are, however, some few cases in which 

 \] c is indefinite, the temperature gradient gradually decreasing, but never reaching 

 zero. In such cases H c is measured to the point (excluding the inversions in the 

 lower strata) where the gradient becomes less than 1 0. per kilometre. The region 

 above this has had various names given to it, viz., the "isothermal region," or more 

 usually the " isothermal," the stratosphere proposed by M. TEISSERENC DE BORT, or 

 the " advective region " by Messrs. GOLD and HARWOOD. The first is the most 

 common, but the region is not isothermal laterally though nearly so, as far as it has 

 been explored, in the vertical direction. 



Annual Variation in H c . 

 The actual mean value of H c for each month is given below in kilometres : 



Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 

 11'8 10*5 107 9'8 1T6 10'3 121 11'8 14'0 127 10'4 97 



but H e is so dependent on the height of the barometer that it, far more than the 

 monthly temperature, requires correction. 



The necessary data for correction are given subsequently (p. 265), and we get : 



Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 

 11-3 10'5 107 10'8 1T9 10'9 10'9 11'5 13'3 12'0 11'2 107 



The values for May and September are discordant, but the causes previously stated 

 vitiate the value for May, and a paucity of observations in September make the 

 value 13'3 for that month of little weight. StiU the four observations for September 

 are well distributed, and it is noteworthy that whereas Messrs. GOLD and HARWOOD 

 found an especially low value for September, the British Isles show an exceptionally 

 high value. Smoothing May and September by the formula a + b + c , and then 

 putting into a sine curve with an annual period, we get : 



Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 

 0-6 10-5 10-6 10-9 11-2 11'4 11'6 1T6 11'5 1T3 1TO 

 The second and third terms of the Fourier series are not taken into account, for 

 ons previously stated. The figures refer to the middle of each month, and 

 mnimuiu occurs at the beginning of March, the amplitude is 0'55, and the 

 mean in km. 



