533 



evident that in order to register the maximum amount of ozone a 

 dark box is required. 



Test-slips. Paper- slips being so fragile, I have substituted others 

 made of calico. The calico is to all intents and purposes chemically 

 pure, containing only a few granules of starch, used in the first pro- 

 cess of its manufacture, which it is very difficult to remove, being 

 enveloped in the cotton fibre ; it is, however, thought to be purer than 

 the paper that is used for these test-slips, every precaution having 

 been taken to make it so. 



Results of observations. The following Tables have been con- 

 structed from observations made between the 1st of May, 1859, and 

 the 31st of March, 1860. 



TABLE I. 



Mean amount of Ozone observed from Test-slips hung for twelve 

 hours, both at night and in the daytime, in comparison with others 

 hung for twenty-four hours. 



The ozone being always in excess in the night, and the tests exposed 

 for twenty-four hours showing always an excess over those only ex- 

 posed for twelve hours. 



