138 ANNUAL OF SCIENTIFIC DISCOVERY. 



tains; and that the variations in the quantity of dew that falls at 

 night, from one season to another, are attended with sufficient varia- 

 tions in the amount of heat imparted to the earth, to effect the changes 

 observed in the nocturnal decrease of temperature during the year. I 

 consider that in the average of months the amount of dew deposited 

 from hour to hour during any one night, and from night to night, must 

 increase steadily from sunset to sunrise, and from summer to winter. 

 It follows from these conclusions that the probable cause of the secon- 

 dary variations of the horizontal force is to be found in the varying 

 quantities of dew deposited from one hour to another, and from one 

 season to another." After some further remarks, Professor Norton 

 shows that the actual effects of dew will, in particular cases, account 

 for the variations observed between his theory and the results as at 

 first found, or in other words, it will account for the discrepancies be- 

 fore referred to. 



He next comes to the diurnal variations of the vertical mngnetic in- 

 tensity. The general theory is that the vertical intensity is proportion- 

 al to the difference of temperature of two places situated at equal dis- 

 tances to the north and south of the station of the needle, and on a line 

 perpendicular to the isogeothermal line. He finds that the actual state 

 of things agrees at least approximately with his theory. There is, how- 

 ever, a slight discrepancy here also, for we find that the variations in 

 the vertical intensity are generally less for the first and last than for 

 the other two quarters of the year, while there is not an equal propor- 

 tionate difference in the variations of temperature. This discrepancy 

 is probably owing to this, that instead of taking the difference between 

 the temperatures at the earth's surface, we should take the difference 

 between the average temperatures of the stratum just below the sur- 

 face, which is subject to a daily variation of temperature. This must 

 be settled, however, by further investigation. 



The last subject treated of is the diurnal variations of the declina- 

 tion. In this particular the general theory is, that the needle is near- 

 ly perpendicular to the isogeothermal line, that is, that the mean 

 position of the needles is at right angles to the ideal line passing 

 through those places which have the same mean annual temperature. 

 This, Professor Norton considers to be also rendered probable by vari- 

 ous facts which he states. He has some very correct remarks to the 

 effect, that no theory should be rejected because, while it seems to ac- 

 cord with facts in all its important points, there are some minor discre- 

 pancies. 



ON THE DIRECT PRODUCTION OF HEAT BY MAGNETISM. 



AT the meeting of the Royal So iety of London, on the 24th of 

 May, W. R. Grove, Esq., read an interesting paper " On the Direct 

 Production of Heat by Magnetism." The author recites the experi- 

 ments of Marrian, Beatson, Wertheim, and De la Rive, on the phe- 

 nomenon which was discovered some years ago, that soft iron, when 

 magnetized, emits a sound or musical note. He also mentions an 

 experiment of his own where a tube was filled with the liquid in 



