654 



THE NATIONAL GEOGRAPHIC MAGAZINE 



reous form, it was a non-conductor of 

 electricity, thus differing in a remarkable 

 degree from tellurium, which was a good 

 conductor. 



When, however, selenium was heated 

 almost to the fusing point and then al- 

 lowed to cool very slowly, it completely 

 changed its appearance. It acquired a 

 dull metallic look, like lead ; and in this, 

 its crystalline condition, was also found 

 to be a conductor of electricity, but of 

 extremely high resistance. A little pencil 

 of crystalline selenium not much more 

 than an inch in length offered as much 

 resistance to the passage of an electrical 

 current as 96 millions of miles of wire, 

 enough to reach from here to the sun, 

 and yet it was a conductor. That was a 

 discovery. Now comes an invention. 



Willoughby Smith, in laying the At- 

 lantic cable, found it advisable to balance 

 the electrical resistance of the cable dur- 

 ing the process of submersion by tre- 

 mendous coils of well-insulated wire. 

 Why, thought he, should not a little bit 

 of selenium balance the whole cable and 

 enable us to get rid of all this complica- 

 tion of wire. 



He succeeded in doing this, but found 

 the electrical resistance very variable. At 

 times the selenium would balance the 

 whole cable and at other times not one- 

 half of it. 



He did not stop with this observation, 

 but sought the cause of the variation. 

 He multiplied observations, and his as- 

 sistant, Mr. May, soon discovered that 

 the resistance of the selenium was greater 

 at night than in the day. 



This at once suggested to Willoughby 

 Smith the thought that perhaps the elec- 

 trical resistance of selenium was affected 

 by light, and he proceeded to put his idea 

 to the test of experiment. He shut up 

 the selenium in a dark box near a bright 

 light, and found that when the lid was 

 open the resistance went down and when 

 it was closed it rose again. Even a 

 shadow falling upon the selenium affected 

 its electrical resistance. 



SPEECH FROM A SUNBEAM 



Then other scientific men took the mat- 

 ter up. Professor Adams, of King's Col- 

 lege, England, discovered that the resist- 



ance varied directly with the intensity of 

 the light that fell upon the selenium. 

 Then I came along with some specula- 

 tions concerning the possibilities of tele- 

 phoning without wires by varying the in- 

 tensity of a beam of light by the action 

 of the voice, and allowing the light to 

 fall upon a piece of crystalline selenium. 

 In this way I thought it would be possi- 

 ble to get speech from a sunbeam. 



Well, I need not go into the details, 

 but it was true. I produced the photo- 

 phone, an instrument for talking along a 

 beam of light instead of a telegraph wire. 

 It is interesting to remember that all 

 these things resulted from the observa- 

 tion of a smell. 



When I was invited to talk to you to- 

 night I had no idea of what to say. I 

 thought of all the good maxims for your 

 future conduct in life ; but giving advice 

 to young people is out of my line, and it 

 seemed to be better to choose some sub- 

 ject with which I was a little familiar 

 myself. 



How discoveries and inventions arise 

 from the observation of little things is 

 surely a topic worthy of your considera- 

 tion. I also thought it would be interest- 

 ing for you to know how many appar- 

 ently impossible results have been actually 

 achieved by the patient multiplication of 

 little observations. 



It was only a short time ago that if 

 you wished to express the idea that any- 

 thing was utterly impossible you would 

 say, "I could no more do that than I 

 could fly." I don't think there is any one 

 here who is too young to have heard that 

 expression. It was the height of impos- 

 sibility that we should fly, and here men 

 are flying in the air today. 



It is only a few years since the first 

 man flew, and we are only at the begin- 

 ning of aviation. What a delightful idea 

 it is to go sailing through the air. The 

 only trouble is that you must come down, 

 and we have altogether too many fatali- 

 ties connected with the work. Here, 

 then, is a subject for you to explore : 

 How to improve the safety of the flying 

 machine. How to produce flying ma- 

 chines that any one can fly. 



We know perfectly well that the time 

 is coming, and is almost here, when it will 



