126 Report S.A.A. Advancement of Science. 



In Sweden the formula is (or rather was, down to 1881, or 

 later) for a Glaisher Screen, 



1/,- (VIII. + XIV. + 5-XXI). 

 At Gaboon, 



'j^- (VII. + XIV. + 2XXI). 



At Magdeburg, 



From May to August. V^- (VIII. + XX. + M -f m). 



From September to April, '/i.,- (s^VIII. + 5-XX. + 

 2-XIV.); 

 and so on, in endless variety. In the British Islands, " the meaii 

 tempeiature of the month for the stations of the Royal Meteoro- 

 logical Society is determined by adding together the mean maximum 

 and the mean minimum, and dividing the sum by 2 " ;* but in 

 most months the resulting value is slightly greater than the hourly 

 mean. 



At the foot of Table 3 will be found the monthly and annual 

 deviation of the mean hourly temperature from the mean minimum, 

 m, the mean maximum, M, and from the average of these two 

 -^■(m + M). As an example, the average of the maximum and 

 minimum shade temperature during June at Klerksdorp was found 

 to be 54'-''o. The correction necessary to reduce the June values 

 to the true mean is ■ — I'^'d, 



••• 54°-o — iO-6 = 520-4. 

 is the mean June temperature required. 



Kaemtz procured a mean temperature \)\ multiplying the mean 

 range M — m, by certain monthly numerical co-efficients, and adding 

 the result to the minimum. Thus : 



T = m + K (M — m), 



where the co-efficient. K, changes in value from one month to 

 another. The monthly values of K. for Kenilworth, together with 

 some comparative numbers for the Northern Hemisphere, are given 

 in Table 15. Sir John Herschel's account of such factors deserves 

 to be put on record as being perhaps the one hopelessly unintelligible 

 sentence he ever wrote : — " Kaemtz recommends (from a discussion 

 of the observations at Padua and Fort Leith . . . ) to employ 

 the formula 



n)-f''.5,. • (M — m) . (5-076 -i-x) 



where x is a variable co-efficient, fluctuating from o"366 in December 

 to o"56o in August; and which may, for the purpose in question, 

 be taken quite near enough at 0-44 sin {6 + 120°), 6 being the 

 sun's mean longitude." 



*Marriott, " Hints to Meteorolojiical Observers," p. 30. See also some 

 remarks by Scott, '' Instructions in the use of Meteorological Instruments," p. 79. 

 Glaishers's elaborate " Diurnal Range Tables " should also be consulted. Hann 

 notices the approach of the average extreme temperature, .} (m + M), to the true 

 mean in October and November :— '• Der Sprung in den Differenzen vom 

 September zum Oktober ist sehr merkwiirdig. . . ." 



