18 METEOROLOGICAL OBSERVATIONS 



months, March and October (31 and 32 per cent.) have the 

 highest, and January and December the lowest percentages (21 

 and 18) of possible sunshine. In the whole year we have an 

 average amount of 1592 hours, or not much more than a third 

 of the actual sunshine above the level of the clouds. 



The Amounts of Nitrogen as Ammonia and Nitrates, Chlorine, 

 and Sulphuric Acid, in. the Rain-water at Rothamsted. 



At the time of the commencement of the Rothamsted 

 Experiments very little was known as to the amounts of com- 

 bined nitrogen and other substances present in rain-water. 



The presence of ammonia, both in the atmosphere and in 

 rain-water, was well known, but, owing to the imperfections of 

 the methods of analysis then available, somewhat exaggerated 

 ideas prevailed as to the amount. Liebig considered that the 

 atmosphere was able to furnish the average crop with sufficient 

 ammonia for its development, hence followed his celebrated 

 " mineral " theory that to add to the soil the ash constituents 

 of a crop would be a sufficient manuring. As this opinion of 

 Liebig's was strongly contested by the Rothamsted investi- 

 gators it was necessary to make accurate measures of the 

 combined nitrogen brought by the rain. 



The earliest analyses of Rothamsted rain were made in 

 1853-4, and were restricted to determinations of the nitrogen 



o 



present as ammonia. These were followed in 1855-6 by 

 determinations of ammonia and nitric nitrogen made by 

 Professor Way. No further analyses were made until 1877, 

 when monthly determinations of ammonia were recommenced. 

 These were continued with some interruptions until December 

 1885, and again resumed by the late Dr Miller in December 

 1887 and February 1888, since which time until December 

 1916 ammonia was regularly determined each month. Dr 

 Miller also determined nitric acid uninterruptedly from 

 September 1886 till December 1916, for the first few months 

 by Schloesing's method, and subsequently by Williams' zinc- 

 copper couple method. 



