1867.] 



On Variation of Magnetic Declination. 



59 



It enables us to y-nderstand why in a well-fed body it may be some 

 time after nitrogen is cut off before the muscles have any difficulty in 

 obtaining what they want, and why in a body ill-s applied with nitrogen 

 exertion lessens, or if kept up produces bad effects. 



If exertion is persevered in under such circumstances, a failure 

 somewhere is always observed. Frequently the nervous s^^stem or the 

 heart shows signs of weakness, a result which could hardly be explained 

 by the view of the Swiss Professors. It is certainly an argument for 

 the viev\- 1 have advocated, that it is in harmony with the teachings of 

 experience, and restores to the rules of diet their old significance. 



X. "Note on the Lunar-diurnal Variation of Magnetic Declina- 

 tion/' By J. A. Broun, F.E.S. Received May 11, 1867. 



Lausanne, 7th May, 1867. 



I received late last night No. 91 of the Proceedings of the Eoyal 

 Society, and desire to offer the following remarks on the abstract 

 of a paper by Mr. Neumayer which I find therein (vol. xv. p. 414). 



Mr. Neumayer is evidently unacquainted with the Note by me, read to 

 the Eoyal Society of London in 1861 (Proc. Eoy. Soc. vol. x. p. 475), in 

 which I stated as result of the discussions of five years' observations at 

 Trevandrum (near the magnetic equator) that the lunar-diurnal varia- 

 tion of magnetic declination became inverted, like the solar-diurnal 

 variation, when the sun passed from one hemisphere to the other, 

 both the solar- and lunar-diurnal variations depending on the position 

 of the sun. 



I also stated the laws of the lunar-diurnal variation, not only for 

 the moon north and south, as Mr. Neumayer has done, but also for 

 the moon on the equator moving northwards, and again on the equator 

 moving southwards, the laws being different for the moon in the same 

 position according as she was moving in one direction or in the other. 



I pointed out in the Transactions of the Eoyal Society of Edin- 

 burgh (vol. xviii. p. 354), that the reversal of movement of the declina- 

 tion-needle with the sun north and south of the equator, observed 

 within the tropics, had its equivalent in the different ranges of the 

 solar- diurnal variation for summer and winter in high latitudes. It 

 followed in like manner that, the lunar-diurnal variation being inverted 

 with the solar-diurnal variation near the equator, a similar difference 

 of ranges should be observed in the laws of lunar-diurnal variation for 

 summer and winter in the higher latitudes. Of this fact I satisfied 

 myself by a rediscussion of the Makerstoun observations, after re- 

 jecting the large disturbances. 



Another consequence of the law of inversion of the lunar-diurnal 

 variation near the equator with the sun's passage from one hemi- 

 sphere to another, and with the inversion of the solar-diurnal varia- 

 tion, was the opposition or approximate opposition of the mean curves 



