488 Dr. 0. Chree : Results obtained at Keiv Observatory with 



Thus no inference can be drawn from the results for any 

 particular type of cloud without considering the corresponding- 

 results from all days of observation. This comparison is 

 made in Table IX. It gives the number of days of each 

 class, the corresponding mean amount of cloud and the per- 

 centage of occasions in which the value of a + , a_, or P was 

 above the average derived from all days of observation in the 

 month to which the observation belonged. The results are 

 given to the nearest 0*5 per cent. 



Table IX. 



Type of day. 



Number 

 of days. 



Mean 

 amount 

 o!' cloud. 



Percentage of cases when 

 Talue above the monthly mean. 



a + . 



a_. 



44-5 

 41 

 51 

 39 



P. 



42 

 30-5 

 31 

 40 



All days 



411 5-8 44-5 



Days of Stratus 



„ Cumulus 



,, Cirro-stratus. 



50 



88 

 85 



9*0 

 5-1 

 5-4 



47 



38-5 



4fi 



In the cases of cumulus and cirro-stratus the mean amount 

 of cloud is less than the mean from all days, but the difference 

 is not large, so that any conspicuous peculiarity in the results 

 for either class, if not " accidental," is presumably really 

 dependent on the type of cloud. We thus infer that the 

 presence of cumulus has a distinct tendency to be associated 

 with low values of P and of a + , but with high values of a_ 

 and so of q. The presence of cirro-stratus seems to have 

 exactly the opposite effect so far as dissipation is concerned, 

 but the apparent association with high values of a + is at least 

 doubtful. The apparent depression in P is also too small to 

 possess much significance. Stratus appears to be associated 

 with a slight rise in a + and fall in a_, and a very decided 

 fall in P. The amount of sky covered on days of stratus is, 

 however, much larger than on an average day, so that the 

 apparent effects on P and a + may be due to the quantity of 

 cloud and not to its type. The examples of stratus were 

 mostly from the winter months, and so from the season when 

 Table VI. makes the influence of cloud on P largest. 



§ 11. Amongst the other meteorological conditions con- 

 sidered were bright sunshine (as opposed to faint or no sun- 

 shine), clearness of the atmosphere (as opposed to haze or 



