TRANSACTIONS OF THE SECTIOXS. 49 



to another, as illustrated by the well-known experiment of M. Fusinieri. Mr. 

 Tomlinson rejected the photo-electric theory, by which M. Poey attempted to 

 account for the production of all these figures. 



Meteorology. 

 On the Causes of the Phenomena of Cyclones. By I. Ashe. 



I 



On the supposed Connexion hettoeen Meteorological Phenomena and the Varia- 

 tions of the EartKs Magnetic Force. By John Allan Broun, F.B.S., Di- 

 rector of the Trevandrum Observatory. 



In the ' Comptes Rendus ' of the French Academy of Sciences for May 6, 1861, 

 a note appeared by Father Secchi, Director of the Observatory of the Roman Col- 

 lege, on the connexion between meteorological phenomena and the vai'iation of 

 the earth's magnetic force, as shown by the bifilar magnetometer at Rome. The 

 results of Father Secchi's discussions appeared to me extraordinary; for though 

 no careful examination of the subject has been published, yet the question had 

 been examined by myself during the years that I directed the Makerstoim Observa- 

 toiy, both while observing, when during two years, on an average of eight hours 

 daily, my eye was upon all the magnetical and meteorological variations, and after- 

 wards whUe discussing the observations. In the latter case the simple method of 

 "rojecting the simidtaneous magnetical and meteorological observations employed 

 y Father Secchi was also used, and had any slightly marked relation existed it 

 woidd have been perceived at once. A particular discussion was made to de- 

 termine if the variations of the external temperature had any effect on the bifilar 

 observations, and the conclusion was that they had none *. 



It would appear, however, fi-om Father Secchi's discussion of the Roman obser- 

 vations, that the horizontal force of the earth's magnetism increases when the 

 north wind blows and the barometer rises at Rome, while it diminishes when the 

 south wind blows and the barometer falls ; the two latter phenomena, it is well 

 known, are connected with each other and with a rising temperatm-e, while the 

 two fonner are connected with a falling temperature. Had the vaiiations of in- 

 tensity to be explained been small, this last relation would have been taken by 

 me as an explanation of the whole discussion, especially as the teniperature-co- 

 efiicient indicated for the Roman bifilar (xto^fot of the whole horizontal force t) 

 is less than half the average coefficient for bifilar magnets. Observations imcoiTected, 

 or insufficiently corrected for temperature would give just such results as those 

 obtained from the Roman bifilar. The variations of force it seems, however, are 

 too large to be explained by any such error X ; and my own unpublished negative 

 conclusions, however satisfactory to myself, cannot be accepted by others in oppo- 

 sition to results so positive as those contained in the paper imder consideration. 

 I have iu consequence undertaken a special discussion of the observations of the 

 bifilar magnetometer and of the anemometer made at Makerstoun in Scotland in the 

 year 1844 §. 



Before entering upon this discussion I should allude to an objection to Father 

 Secchi's results, which exists in the conclusions of a paper by me on the horizontal 

 force of the earth's magnetism, lately printed in the * Transactions of the Royal 

 Society of Edinburgh' ||. From this paper it appears that generally, when the 

 daily mean horizontal force diminishes at one point on the earth's surface,^ it 

 diminishes simultaneously, and by nearly the same amount, at all other places (the 

 discussion includes stations between 55° north and 42° south latitude) ; the same 



* Trans. Roy. Sec. Edinb. vol. sviLi. Introduction, 

 t Comptes Rendus, lii, p. 907. | Ibid. p^907. 



§ Trans. Roy. Soc. Ediab. vol. xviii. 

 II Ibid. vol. xxii. p. 511. 

 1861. 4 



