94 Ml*. J. A. Broun on Terrestrial Magnetism. 



lines of force upwards and increases the dip " (Phil. Trans, 

 p. 112, 1851). 



According to Dr. Faraday's hypothesis, then, the variation of 

 dip should be zero where the dip is zero. The law of diurnal 

 variation ought to be opposite on opposite sides of the magnetic 

 equator, and different on the north side of the magnetic equa- 

 tor, within the tropics, from that where the dip equals that at 

 Hobarton (at Makerstoun, for example) and "the region is 

 within the angle formed by the line of dip with the horizon. '^ 

 Now none of these conclusions are true. 



There ought also to be some test in this place. Let us take 

 the month of March for instance. The sun is nearly vertical ; 

 there has scarcely been a cloud seen since December ; the tem- 

 perature is near its maximum ; the soil is red, and heated gusts 

 of air pass as if escaped from a furnace. In October, on the 

 other hand, the temperature is a minimum ; the sky has been 

 overcast for months, one monsoon has passed and shed its rain 

 in deluges, and another is in full force. The lower stratum of 

 air, a mile deep, is sheltered from the direct rays of the sun, and 

 there is an atmospheric shell in the condition of paramagnetic 

 polarity : ought there not to be a marked difference in the varia- 

 tions during these two months ? and yet there is little or none. 



I have now, in correspondence with his Highness the Rajah 

 of Travancore's observatory here, another observatory on the 

 highest and sharpest peak of our Ghats, supported also by His 

 Highness the Rajah. You will see from the report published, 

 of which I have sent you a copy, an account of the ei'cction 

 of this observatory. It is exposed for some months to the 

 sun that is burning up the eastern side of the Peninsula, while 

 the western side, Travaucore, is covered by a sea of vapour. I 

 have a series of observations, magnetical and meteorological, 

 made on this peak hourly dui'ing upwards of two years. Froin 

 these observations 1 believe I shall be able to add further evi- 

 dence of the complete insufficiency of any temperature theoiy in 

 accounting for the magnetic variations. 



The following I shall offer partly in the form of questions : — 



Does not the sun act as a magnet, perhaps as an electro-mag- 

 net, the currents forming it bemg within its atmosphere ? Are 

 not the solar spots disruptions of the current due to the posi- 

 tions of the planets with reference to the plane of its equator ? 

 After a magnetic disturbance there is a diminution of force shown 

 on the earth, which remains for some days as if there had been a 

 violent action with the result of a loss of energy. The con- 

 nexion of the solar spots with the frequency of the aurora 

 borealis (and therefore, as we now know, with the magnetic dis- 

 turbance) was remarked by Mairan [Traite, &c. p. 264, 2nd edit.), 



