1882.] Temperatures of the Water of the Thames, fyc. 279 



Table I. — Monthly Mean Temperature of the Water of the Thames. 

 Table II. — Monthly Mean Atmospheric Temperature at the Royal 

 Observatory. 



Table III. — Monthly Mean Excess of Thames Temperature above 

 Observatory Atmospheric Temperature. 



Table IV. — Monthly Mean of Diurnal Range of Temperature of 

 the Water of the Thames. 



Table V. — Monthly Mean of Diurnal Range of Atmospheric Tem- 

 perature at the Royal Observatory. 



And the following appear to be the legitimate epitomized inferences : 



(1.) The mean temperature of the Thames water is higher than 

 that of the Observatory thermometers by 1 0, 5. But the locality of 

 the Observatory thermometer is, in hypsometrical elevation, about 

 160 feet above that of the Thames thermometers. It would seem 

 probable, therefore, that the mean temperature of the water is higher 

 than the climatic temperature by only a small fraction of a degree. 



(2.) This difference is not uniform through the year. With some 

 irregularities, the greatest excess of Thames temperature occurs in 

 October and the least in February. But the autumnal difference 

 exceeds the spring difference by only 1°'8. It seems not improbable 

 that this is the effect of a slight communication with the sea, whose 

 surface-waters have accumulated in autumn the effect of solar radia- 

 tion through the summer ; with contrary effect at the opposite season. 



(3.) The mean range of temperature through the day is 2 0, 1, and 

 this expresses the numerical change from the lowest solar tempera- 

 ture, or the lowest temperature in the first tide, or the lowest tem- 

 perature in the second tide (whichever may be the lowest), to the 

 highest solar temperature, or the highest temperature in the first tide, 

 or the highest temperature in the second tide (whichever may be the 

 highest). It is evident that the change of temperature due to the 

 diurnal change of solar action, and the change of temperature due to 

 each of the tides, must each, individually, be very small. 



(4.) It appears to me that the fundamental inference must be this : 

 that the material water is very little changed at Greenwich by the 

 tide. Although a vast body of water rushes up at every flow, running 

 with great speed, and sometimes raising the surface by 20 feet, yet 

 nearly the same water runs down at ebb, and is again brought up, 

 with all its contents, at the next flow. These expressions are to be 

 taken as modified by the descent of fresh water from the land ; but 

 the amount of that water must be small in comparison with the mass 

 which it joins in the Thames at London. 



(5.) I do not imagine that the tidal action has any beneficial effect 

 on the climate of London, except that probably the agitation of the 

 water produces mechanical agitation of the air, and thus destroys 

 injurious stagnation. 



vol. xxxiv. u 



