NEW CONCEPTIONS IN SCIENCE 



which, save for our new mechanical senses, we 

 should never have been conscious of but one. 



The ear hears little of what is going on around 

 us. By means of a microphone the tread of a fly 

 sounds like the ramp of cavalry. Our heat sense is 

 very vague ; we need a variation of at least one-fifth 

 of a degree on a thermometer to realize any dif- 

 ference in temperature. Professor Langley's little 

 bolometer will note the difference of a millionth 

 of a degree. It is two hundred thousand times as 

 sensitive as our skin. A galvanometer will flex 

 its finger at the current generated simply by de- 

 forming a drop of mercury pressing it out from 

 a sphere to the shape of an egg. The amount of 

 work done by a wink of the eye would equal a 

 hundred billion of the units marked on the scale 

 of a very delicate instrument. It is at least ten 

 thousand times as sensitive as the eye or the ear. 

 But even this astonishing performance is far sur- 

 passed by the exquisitely sensitive coherers, dis- 

 covered by Professor Branly, of Paris, by which 

 the Hertz waves of wireless telegraphy are caught 

 in their pulsings through space. And these, in turn, 

 seem clumsy and coarse beside Professor Ruth- 

 erford's magnetic detector, which made possible 

 Signor Marconi's first sending of actual messages 

 across the Atlantic; or the "hot wire" receiver in- 

 vented by Professor Reginald A. Fessenden. The 



304 



