[In the last edition of the 'Fragments of Science an essay 

 on * Dust and Disease ' followed here ; but as almost all my 

 writings on the ' Germ Theory ' are now collected in a single 

 volume entitled ' Essays on the Floating Matter of the Air,' 

 * Dust and Disease ' no longer appears in the * Fragments.' In 

 its place I venture to introduce a short article written early 

 last year for an important American magazine.] 



V. 

 THE SKY. 1 



INVITED to write for the * Forum* an article that 

 would have brought me face to face with ' problems of 

 life and mind ' for which I was at the moment unpre- 

 pared, and unwilling to decline a request so courteously 

 made, I offered, if the editor cared to accept it, to send 

 him a contribution on the subject here presented. 



I mentioned this subject, thinking that, in addition 

 to its interest as a fragment of ' natural knowledge,' it 

 might permit of a giance at the workings of the 

 scientific mind when engaged on the deeper problems 

 which come before it. In the house of Science are 

 many mansions, occupied by tenants of diverse kinds. 

 Some of them execute with painstaking fidelity the 

 useful work of observation, recording from day to day 

 the aspects of Nature, or the indications of instruments 

 devised to reveal her ways. Others there are who add 

 to this capacity for observation a power over the 

 language of experiment, by means of which they put 

 questions to Nature, and receive from her intelligible 

 replies. There is, again, a third class of minds, that 

 cannot rest content with observation and experiment, 

 1 From ' The Forum,' February 1888, 



