C. GENERAL PHYSICS. I49 



carbon have but little magnetic tenacity, while those that 

 have a medium amount of carbon become elastic and resist 

 the attempt to magnetize them. The soft steel is, of all other 

 substances, that which takes up the greatest temporary mag- 

 netism. The tempered steel receives far less, but holds it 

 more energetically. By the coefficient of polarity, Jamin 

 means the ratio between the force of attraction shown by the 

 magnet and its length or mass. He finds this coefficient to 

 vary remarkably with the temper and annealing of the steel ; 

 so that, in almost every case, the steel that has been temper- 

 ed by heating it up to a cherry red has about thirty per cent, 

 greater capacity for magnetism than that which has been 

 heated up to the second blue tint. The rule, however, holds 

 only for the English steel. That which comes from certain 

 steel works in France follows a directly contrary rule, in- 

 asmuch as in these cases the steels that have been highly 

 tempered have a greater capacity for magnetism than those 

 tempered at low heat.-=^ B^ 1873, 90. 



TEERESTKIAL MAGNETISM AND BAROMETRIC FLUCTUATIONS. 



Mr. J. A. Broun has advanced the theory that there is a 

 connection between barometric variations and those of ter- 

 restrial magnetism. He first endeavors to show that great 

 barometric depressions are produced, simultaneously, in va- 

 rious parts of the equatorial seas ; that they have a period of 

 twenty-six days, and are dup to a direct action of the sun ; 

 that there is also a periodical maximum of the magnetic 

 force, following two and a half days after the barometric 

 maximum. Broun then proceeds to compare the records at 

 two antipodal stations, and shows that the respective baro- 

 metric variations follow similar laws, so that the maxima oc- 

 cur on the same daj'- at both stations in twenty-six-day cy- 

 cles, of which fourteen make one mean solar year. The am- 

 plitude of the barometric oscillation is one fourth of an inch. 

 These results are based upon the published hourly obser- 

 vations at Makerstoun and Hobart-Town in 1844 and 1845, 

 as made in accordance with the svstem of investicration into 

 terrestrial magnetism pursued by the British government in 

 those years. Mr. Broun finds his conclusions also verified by 

 a study of the observations at Greenwich Observatory dur- 

 ing the past twenty years. 6 i?, 1873, G95. 



