for the year 1871. xlix 



points, and very careful examination of the polarisation of 

 the coronal light. 



Recent applications of the spectroscopic science include the 

 employment of the salts of lithium for determining questions 

 concerning sewage, contamination of drinking water, and the 

 possible spreading of cholera, typhoid fever, and like diseases. 

 The spectrum of lithium, as you are aware, is of an exceed- 

 ingly well marked and unmistakeable character. It is, 

 moreover, readily obtained from the slightest traces of the sub- 

 stance. To the suspected cesspool or sewer an addition of a salt 

 of lithium is made, after which, by examining contiguous 

 supplies of drinking water in the spectroscope, the presence 

 or absence of the lithium line shows unequivocally whether 

 contamination by infiltration has or has not taken place. 



Among works of art paintings are remarkable for their 

 perishable character, their decay in many instances arising 

 from the very nature of the pigments and vehicles employed. 

 The works of Sir Joshua Reynolds and those of the great 

 Turner afford lamentable instances of decay resulting from 

 the empirical handling of the painter's materials, but to the 

 present hour little or nothing has been done to set the 

 manufacture and use of pigments upon a proper chemical 

 basis. Within the last year, however, a step has been made 

 by the Royal Academy of Great Britian, which has founded 

 a professorship of chemistry in its application to the fine arts, 

 fi'om which we may hope that the evil referred to will be 

 gradually overcome. 



Early last year the scientific world were very much 

 interested in the results of some experiments by Professor 

 Tyndall on the dust which pervades the air we breathe. We 

 had been accustomed to look upon the numberless motes which 

 can be seen floating in the air wherever a beam of strong 

 light traverses it as merely dust — organic, or inorganic, but 

 at least, innocuous matter ; but Professor Tyndall showed 



