When it comes to the temperature normally measured by meteorologists - the "temperature in the shade" - there is little difference between town and country on a sunny, summer morning.
Indeed, it is not unknown for the shade temperature in the city to be a little lower than in the surrounding countryside in the forenoon, because of the slight attenuation of the city sunlight by the dust and smoke endemic in the urban atmosphere.
But city streets can sizzle in the afternoon. For the pedestrian walking the pavements in the sunshine, the intrinsic warmth of the air is augmented by the heating effect of the direct sunlight beating down from overhead. More energy is reflected in his or her direction from the brightly painted surfaces of nearby buildings.
Added to these is the fact that the incessant stream of solar energy causes the temperature of streets, footpaths and south-facing buildings to soar to perhaps 40 or 50 degrees. All these surfaces reradiate their heat in the direction of the unfortunate passerby, who might by now be compared to a Christmas turkey turning in a slow oven.
To make matters worse, the surrounding buildings break up the cooling effect of breezes, that might offer some relief.
As the day progresses, the brick and concrete of the buildings, and the compacted soils beneath the city roads and parking areas, act like giant storage heaters to store the received energy. In this they are quite unlike the relatively loose and "air-filled" soil of agricultural land.
In addition, if there be showers, the efficient and very rapid drainage of surface water in the city means that less energy is dissipated through evaporation than if the liquid was allowed to lie; the significant decrease in temperature which accompanies this in the country is virtually absent in the urban environment.
The city continues to hold the heat it has accumulated well into the late evening. As night falls, the streets and buildings start to cool. The heat absorbed during the day is retained for a time, and released slowly during the hours of darkness - "at midnight," as Thomas Hardy puts it, "when the noon-heat breathes it back from walls and leads".
This prevents the night-time temperature from falling as low as otherwise it might; by morning this excess heat has not entirely expended itself, and if the sunny spell continues, the next sizzling day begins with a literally "built-in" thermal advantage - or handicap, depending on how you wish to look at it.