384 Royal Society :— 



(The nature of the metal may be altered otherwise than chemi- 

 cally.) 



If the temperature of the metal vary in auy way throughout its 

 length, then if it be homogeneous, the electromotive force will depend 

 only on the temperatures of its extremities. 



In a circuit of one metal, the author considers that at the junction 

 of the ends there may be a real discontinuity of temperature while 

 there is a continuity of electric current. He regards the explanation 

 of the effect bv the stratum of air between the unequally heated ends 

 to be unsatisfactory. Mercury, as is known, will not produce 

 thermo-currents in this way. The author considers that the texture, 

 fee., as well as the chemical nature of the substance, influences the 

 value of the thermo-electric function. He also shows the possi- 

 bility of the thermo-electric inversions first discovered by Professor 

 Camming. 



May 21. — Major-General Sabine, President, in the Chair. 

 The following communication was read : — 



" On the Nature of the Sun's Magnetic Action upon the Earth." 

 By Charles Chambers. Esq. 



If the sun were a magnet of sufficient power to exert a sensible 

 attraction upon a small magnet at the distance of the*earth, it would 

 have a real influence on the earth by inducing magnetism in its soft 

 iron, and an apparent one due to the direct action of the sun upon 

 the magnets used for measuring the earth's variations of force. As 

 the earth rotates upon its axis, producing a varying relation, as to 

 position, of the place of observation with respect to the sun, a diurnal 

 variation will thus be produced in the forces which act upon the 

 magnetometers, which variation is shown to follow the simple law 

 x=A sin(/< —ol), x being the deviation of the magnet from its normal 

 position, h the hour-angle of the sun (and for a single day), A a con- 

 stant coefficient, and a a constant angle. A comparison of this result 

 with the laws of the observed diurnal variations shows that direct and 

 inducing action of the sun is not the sole cause of the variations. 



An endeavour is then made to prove that if any part of the observed 

 diurnal variations is due to this cause, it is small in comparison with 

 that produced by other forces in operation. This is done by sepa- 

 rating from the observed variations the part of them which obeys the 

 law x'=B sin (A + ,3), and comparing the variations in the values of 

 B and ,3 from month to month with those of A and a, when it is 

 seen that the former obey a law which has but little similarity to the 

 law of variation of the latter. 



June IS. — Major-General Sabine, President, in the Chair. 

 The following communication was read : — 



" On the Measurement of the Chemical Brightness of various por- 

 tions of the Sun's Disc.' ; By Henry Enfield Boscoe, B.A., F.R.S. 



The author has applied the method of measurement of the chemical 

 action of sunlight, which Professor Bunsen and he described in a 



