738 The Outline of Science 



come of everyday practical utility. But man has not been able to 

 devise a light as economical as that of the fire-fly ! 



And yet we cannot pass from this subject without some ap- 

 preciation of the progress that man has made in the art of produc- 

 ing light. It is a sort of index of his ascent. This was well 

 expressed, for the time, by Sir William Crookes's preface to the 

 first edition of Faraday's Chemical History of a Candle. 



From the primitive pine torch to the paraffin candle, how 

 wide an interval! between them how vast a contrast! The 

 means adopted by man to illuminate his home at night stamps 

 at once his position in the scale of civilisation. The fluid 

 bitumen of the Far East, blazing in rude vessels of baked 

 earth ; the Etruscan lamp, exquisite in form, yet ill adapted 

 to its office ; the whale, seal, or bear fat, filling the hut of the 

 Esquimau or Lapp with odour rather than light; the huge 

 wax candle on the glittering altar; the range of gas lamps 

 in our streets all have their stories to tell. All, if they could 

 speak (and after their own manner they can) might warm 

 our hearts in telling how they have ministered to man's com- 

 fort, love of home, toil, and devotion. 



This was well said, but we have had a glimpse of what might be 

 added thereto of incandescent mantles made of rare elements 

 gathered, often laboriously, from the far corners of the earth; 

 of delicate metal filaments whose toughness is such that the resist- 

 ance they offer to the passage of electricity produces a most excel- 

 lent brilliance; and of subtleties on the inventor's horizon which 

 promise still more perfect light. 



A Story about Helium 



The element helium was first detected in the sun by means of 

 the spectroscope. It was twenty-five years later before it was 

 recognised upon the earth. How important and unlooked-for 

 results may follow from scientific investigations and discoveries 

 is illustrated in this case, as in many others. 



Helium is chemically inert ; like argon it unites with no other 



