318 Thermometric and Hygrometric Observations, [June 21, 



considerably warmer than at the top of the tower. The greatest 

 difference is from 9 a.m. to 3 p.m., after which it begins to get less and 

 less. 



On examining the individual readings for each day, two interesting 

 features are clearly brought out, viz., (1) that in fine bright weather 

 the temperature at 4 feet during the day is much higher than on the 

 top of the tower, — in summer the difference sometimes reaches 5° at 

 1 p.m. ; and (2) that in foggy weather the temperature at the top of 

 the tower is always higher than at 4 feet, the upper part of the 

 tower being generally free from fog. In cloudy and wet weather the 

 temperature is uniformly higher in the churchyard than at the top of 

 the tower. 



These observations, however, like nearly all those previously made, 

 refer mostly to the day time ; it was felt of pre-eminent importance 

 that readings should be taken occasionally throughout the night as 

 well as the day. Hitherto the usual difficulties in obtaining observa- 

 tions requiring night attendance have prevented any considerable 

 number of such records being obtained, but every effort will be made 

 to increase their number, especially when extreme atmospheric condi- 

 tions prevail. During last winter there were eight occasions upon 

 which one of the church officials was on duty ail night, and for those 

 periods we have complete records. 



The following are brief descriptions of the weather on each 

 •occasion : — 



November 11-12. Fine clear cold night, followed by a fine day, 

 with slight fog. 

 18-19. Dull, wet and squally. 

 „ 25-26. Fine bright night, dull day, rather windy. 

 December 2-3. Dull, with snow at night, fog in afternoon. 

 9-10. Dull and cold. 

 ,, 16-17. Dull and damp. 

 „ 23-24. Fine and bright, slight fog 5-9 p.m. 

 „ 30-31. Cloudy night, wet day with fog. 

 The temperatures are given in Table III. 



The prevalence of fine clear nights is readily seen by the increased 

 temperature at the upper station ; the presence of fog is also indicated 

 in a similar manner; while cloudy skies, rain, and wind prevent 

 radiation, and so on the days and nights of their occurrence the 

 temperature is always highest near the ground. 



From the foregoing it seems that the difference between the 

 temperature at 4 feet and 260 feet is chiefly regulated by the amount 

 of cloud, and by the relation of the temperature of the surface of the 

 ground to that of the general body of air passing over it. If so, it 

 will follow that the mean difference between the temperature at the 

 two heights can only be determined by very numerous observations, 



