MADE AT CARNWATH, LANARKSHIRE. 287 



(1.) Since the thermometers at Winterlaw are placed in the centre 

 of a circular patch, 50 feet in diameter, cleared of trees, it is evi- 

 dent that, considering the comparatively large portion of unob- 

 structed sky overhead, the influence of solar and terrestrial radiation 

 are very considerably felt at the spot where the thermometers are 

 placed. (2.) Since trees from 30 to 40 feet in height surround the 

 thermometers all round, and since the free circulation of the air is 

 thereby greatly impeded, it is further evident that the effects of 

 solar and terrestrial radiation will tend to accumulate at Winterlaw 

 station to a greater degree than at Gallowhill station. For example, 

 on the last six days of June when light winds prevailed (the average 

 velocity of the wind during the period being only 5 miles per 

 hour), with an average sunshine of 8 hours per day the mean 

 maximum temperature of the six days was 62°«9 at "Winterlaw, and 

 G2°-0 at Gallowhill. Again, from the 7th to the 13th of the same 

 month, when high winds prevailed (the average velocity for the seven 

 days being 21 miles per hour), with an average sunshine of 10 hours 

 per day, the mean maximum temperature for the period was 61°*1 

 at Winterlaw, and 59 o, at Gallowhill. Hence, with very light 

 winds, the temperature of the days was 0°-9 greater in the wood 

 than outside of it ; but with high winds the difference amounted to 

 2°*1. It is scarcely necessary to remark, that it is in very windy 

 weather that the circulation of the air inside the wood is, as com- 

 pared with what prevails outside the wood in the open fields, 

 relatively least. 



During the spring and summer months the great annual in- 

 crease of temperature takes place, owing to the gain by solar radia- 

 tion being greatly in excess of the heat lost by terrestrial radiation. 

 Now it is during this period that, as shewn by the Carnwath obser- 

 vations, the day temperature of confined spaces in woods, to which 

 the sun's rays have access, and where circulation is impeded, most 

 exceeds the temperature outside the wood where the circulation is 

 free all round; and it is to be noted that the difference was greatest 

 in June. During the annual fall of the temperature in autumn, 

 the difference between the day temperatures at the two stations 

 is less marked, and besides it is the station inside the wood 

 at which the temperature is lowest, — the mean difference being O- G 

 in September and o- 5 in October. In September 1873, one of the 

 more marked cases of higher day temperatures at Gallowhill occur- 

 red from the 21th to the 27th October 1873, during which period 

 the air remained all but calm, the mean velocity of the wind 



VOL. VII. PART III. x 



