458 



KEPORT — 1891. 



■water- temperature was nearly a degree below the average (49°' 5). The 

 difference between the average temperature of the warmest and coldest 

 year recorded was only 2°'5 for the water. 



The highest mean temperature of the water for any month was 68°' 7 

 in July 1887, the month of highest air-temperature also, with an abnor- 

 mally low rainfall, but in a year the temperature of which was below the 

 average. The lowest mean temperature of the water was 32°'4 for 

 January 1891 (air 32°'6), but the lowest air-temperature was 29°'2 for 

 December 1890 when the water had a mean of 33°'3. 



The difference in average temperature of water for the same month in 

 different years was greatest in the months of annual maxima and minima. 

 The hottest June was 10°"6 warmer than the coolest June ; the warmest 

 January was 9°'7 warmer than the coldest January. At the time of 

 annual average temperature the difference was least ; thus the warmest 

 April was only 5°'6 and the warmest September only 4°'2 above the 

 temperature of the coldest month of the same name. 



On the average, as shown in Curve XXX., the air-temperature came 

 nearest the water-temperature in the winter months, notably in November 

 and January, when they almost coincided (difference 0°'2), and the two 

 temperatures diverged most in the summer months, particularly April, 

 May, and July, when the difference averaged 2°'3. During the ten years 

 of observation the average monthly air-temperature was higher than the 

 average monthly water- temperature at 9 a.m. on 17 occasions. Of these 

 6 occurred in January, 2 in February, 4 in November, and 2 in December, 

 or 14 in the winter months ; 1 Avas in March, 1 in May, and 1 in October. 

 In no April, June, July, August, or September, between 1882 and 1891, 

 has there been an instance of air being warmer than water on the average 

 of a whole month. Of course, in the remarkably fine observations now 

 recorded the comparison is made between average air-temperature for the 

 whole 24 hours, and average water-temperature at 9 a.m. only, while in 

 the short series of observations specially made for the Committee the air- 

 and water-temperature are both calculated for 9 a.m. 



Mean Monthly Observations on the Temperature of the River Chenvell at 

 Oxford. By Mr. Edward Chapman, Magdalen College. 



