Temperature of the River Nith. 241 



June, and July from i deg. in March to 2.7 deg. in May. There 

 were four months in which the temperature of the air was slightly 

 higher than that of the water, one (November) in which it was 

 ■exactly the same, and seven in which the temperature of the 

 water was highest, but only to a very limited extent, the excess 

 and the deficiencies almost balancing one another. If now we 

 compare the temperature of the river with that of the estuary at 

 Glencaple, we find a different result. The annual means, insteail 

 of coinciding, show an excess of almost i deg. in favour of the 

 estuary, viz., 48.7 deg. The annual mean of the river as ascer- 

 tained by the observations ten years ago, was 48.5 deg., as com- 

 pared with 47.8 deg. The explanation of this is very simple. 

 The observations of the estuary having been taken always at or 

 near high tide, and during the day, would, as a rule, be near the 

 maximum, while those, both of the river and the air, were 

 calculated from the combined maxima and minima of each day ; 

 and then the flow of the tide over a large extent of sand on warm, 

 sunny weather must also necessarily have the effect of increasing 

 the estuary temperature. It may be interesting to bring out the 

 seasonal variations of temperature, both in the river and estuary, 

 as compared with those of the air. Dividing the year into four 

 :seasons — winter, spring, summer, and autumn — with three months 

 ■each, the following table will show the variations: — 



River Water. Estuary. Air. 



Mean temp. Met n Temp. Mean temp. 



Deg. Ueg. Deg. 



December 371] 37 6) 37 ] 



January 381 [365 40 [37-5 39-2J-36 7 



February .34 5 J 34 9 J 34 J 



March 42 8 1 43 ) 438] 



April 4o'2U6 44 UsB 46 [45-7 



May 50 j 50 J 47-3J 



June 57 2] 58-2'| 56 "1 



July 661 [61-6 65-6V61-9 64 6 U9-9 



August 59-9J 62 ij 59-2) 



September ... ... 55 •4] 57*2] 55 •8] 



October 48-5 V.36-5 49-9V37-5 48-3V36-7 



November 40-8J 43-1 J 413] 



From this table it appears that the temperatures of spring — in- 

 cluding March, April, and May — approximate most closely those 

 •of the estuary, and the air differing only by one-tenth of a degree, 

 viz., 45.6 deg. for the estuary and 45.7 deg. for the air, while the 

 jiver has a mean of 46 deg. — the highest of the three by a 



