[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* 



TNYITED to write for the ' Forum ' an article that 

 -L would have brought me face to face with ' prob- 

 lems of life and mind ' for which I was at the moment 

 unprepared, and unwilling to decline a request so cour- 

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

 to send him a contribution on the subject here pre- 

 sented. 



I mentioned this subject, thinking that, in addition 

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

 might permit of a glance at the workings of the scien- 

 tific 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 lan- 

 guage of experiment, by means of which they put ques- 

 tions to Nature, and receive from her intelligible re- 

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

 cannot rest content with observation and experiment, 



* From ' The Forum,' February 1888. 

 131 



