LIGHT-NOON AND THERMAL NOON 



105 



I have recently been able to perfect another clockwork 

 device by which the bent tip of the galvanometer index is 

 periodically pressed against a moving sheet of smoked paper. 

 This simple arrangement eliminates the complications of the 

 spark-record. 



The record given in fig. 30 was taken about the end of 

 January ; the sun rose at about 6.45 a.m. and set at 5.30 p.m. 



Fig. 31. Record of Diurnal Variation of Light and of Temperature 



in Summer 



The twilight is very short in the tropics : the sky is feebly 

 lighted about 6 a.m. ; it becomes dark about 6 p.m. The 

 record shows the intensity of light to have been exceedingly 

 feeble at 6 a.m. The rise in the intensity was rapid, attain- 

 ing the maximum at 12 noon. This will be designated as 

 the light-noon. The intensity of light then declined at 

 a rate slower than the rise. But after 5 p.m. the fall of 

 intensity was extremely rapid. 



It was stated that there is a possibility of change of 



