Tests of Herschel's JEthereal Physics. 255 



12 layers. To the lower end of the suspended wire was fixed a 

 small plane mirror which reflected an indicating beam of light upon 

 an ordinary galvanometer-scale 127 cm. distant from it. Each 

 scale-division was equal to *64 mm. A steady current of about 

 1 ampere was passed through the iron wire from the clamp to the 

 free end, which dipped into a mercury-cup. The magnetizing coil 

 was in circuit with a battery of 7 Grrove cells, a box of resistance 

 coils, a tangent galvanometer, and a contact key. 



The deflections of the spot of light when various currents were 

 passed through the coil are given below : — 



Iron wire unstretched. 

 Current. Deflection. 



0*36 amperes. +7 divisions. 



1-2 „ 



3'7 „ -4 „ 



Same wire loaded with 6*3 kilos. 

 0-33 amperes. -1-2 divisions. 



0'59 „ 



3-68 „ -3 „ 



The current which produced no deflection was obtained tenta- 

 tively by varying the resistance ; a current slightly stronger or 

 weaker than that indicated caused a perceptible deflection in one 

 direction or the other. It will be seen that when the wire was 

 loaded with a weight of 6*3 kilogrammes the current causing no de- 

 flection was reduced to one half of its former value. The deflections 

 given above are those produced by the second and subsequent 

 currents of the strength denoted. That due to the first current 

 was uncertain, depending probably upon the previously existing 

 permanent magnetism of the wire. This point, amongst others, 

 requires further investigation. 



XXX. Tests of Herschel's ^Ethereal Physics. 

 By Pliky Earle Chase, LL.D* 



JEVONS says (' Principles of Science/ ii. p. 145) :— " Sir 

 John Herschel has calculated the amount of force which 

 may be supposed, according to the undulatory theory of light, 

 to be exerted at each point of space, and finds it to be 

 1,148,000,000,000 times the elastic force of ordinary air at 

 the Earth's surface, so that the pressure of the aether upon a 

 square inch of surface must be about 17,000,000,000,000, or 

 seventeen billions of pounds ; yet we live and move without 

 appreciable resistance through this medium, indefinitely harder 

 and more elastic than adamant. All our ordinary notions 

 must be laid aside in contemplating such an hypothesis ; yet 



* Communicated bv the Author. 



