36 



MR DALMAHOY ON A DIFFICULTY IN THE THEORY OF RAIN. 



received at different levels. It is true that the maximum quantity of rain which 

 fell continuously in a given time, cannot be determined by means of this series of 

 observations, for the intervals between the consecutive observations were too 

 long to admit of this ; but still it is possible to assume a value which may be sup- 

 posed, on good grounds, rather to exceed than fall short of the actual maximum 

 rate. The following table* contains an abstract of the winter observations at 

 York to which allusion has just been made. It exhibits the depth of rain which 

 fell into gauges, at three different levels, during a period of 270 days, comprising 

 the months of December, January, and February, of the years 1832-33, 1833-34, 

 1834-35 :— 





Height of the 



Gauge above 



the ground, 



in feet. 



Depth of 

 Kain in 

 inches. 



Ratios of the 



Depths, that 



on the ground 



being 1. 



Ground gauge, 







17-32 



1- 



Museum gauge 



44 



1217 



0-7 



Minster gauge, 



213 



8-65 



0-5 



The remarkable fact to be learnt from this table is, that the Ground gauge 

 received 30 per cent, more rain than the Museum gauge, the difference of level 

 being only 44 feet ; and 50 per cent, more than the Minster gauge, the difference 

 of level being 213 feet. 



As respects the rate at which the rain fell, the table shows that the Ground 

 gauge received 1732 inches in the course of 270 days, — that is, on an average, 

 0064 inches in twenty-four hours. This, of course, is the mean rate for the 

 whole period, including fair and rain}^ weather ; but what is wanted is the largest 

 quantity which fell continuously in a given time. Sir John Herschel states,t that 

 " it is considered, in the greater part of England, a heavy rain if an inch fall in 

 the course of twenty-four hours." Therefore, guided by this, it is proposed to 

 assume, that on one of the 270 days included in the York observations it rained 

 continuously for twenty-four hours ; and that, during this period, the Ground 

 gauge received one inch of rain, the Museum gauge 0*7 of an inch, and the 

 Minster gauge 5 of an inch, — these quantities bearing to each other the same 

 ratios which, as the fourth column of the above table shows, the whole quantities 

 bear to each other. 



Adopting, then, these data, the hypothesis assumes that, on the occasion in 



* Report of Brit. Assoc, for 1835, p. 173. N.B. — The error in the Minster column is corrected. 

 \ Art. Meteorology , par. 115. 



