60 



On the Great Nebula in Orion, 



[June 20, 



of lunar- diurnal variation in tlie higher latitudes of the two hemi- 

 spheres. This conclusion, however evident at the time my note was 

 written (1861), appeared opposed to the fact, since the law of lunar- 

 diurnal variation at Toronto, according to Greneral Sabine's discussion, 

 was an inversal of that at Prague and Makerstonn, all three places 

 in the same hemisphere; this I pointed out at the time (Proc. E,oy. 

 Soc. vol. X. p. 475). This statement seems to have caused a re- 

 examination of the Toronto discussion, as Greneral Sabine afterwards 

 discovered that west had been substituted for east in his original 

 memoir. 



It followed from the similarity of the laws for the sun and moon 

 discovered by me, and, tliis correction made, from the observations in 

 the two hemispheres, that the mean law for a north latitude should be 

 the inverse of that for a south latitude ; or that a maximum of easterly 

 declination in one hemisphere should be simultaneous, or nearly so, 

 with a minimum in the other. 



My chief object now is to draw attention to the fact (published in 

 1861) of the similarity of the cbanges of the laws of solar- and lunar- 

 diurnal variations of the magnetic needle, with the sun's change of 

 declination, as this fact appears to have escaped the notice of those 

 men of science who since then have been engaged in proving inde- 

 pendently the conclusions whicb follow from the note now referred to. 



Mr. ISTeumayer remarbs "that in some cases the lunar-diurnal 

 variation manifests itself in a very striking manner during the winter 

 months." This fact I had already remarked in the discussion of the 

 Makerstoun observations for 1844 and 1845 ; but I have shown in a 

 paper forwarded lately to the [Royal Society of Edinburgh that tlie 

 effect of the lunar action is sometimes greater than that of the solar 

 action ; and this is made evident from the lunar-diurnal variations for 

 single days, as well as in the means deduced from a single lunation 

 (Dec. 1858 to Jan. 1859) for eacb of the four positions of the moon 

 already referred to. 



XI. "An Account of Observations on the great Nebula in Orion, 

 made at Birr Castle, with the 3-feet and 6-feet Telescopes, 

 between 1848 and 1867.'^ By Lord Oxmantoavn. Communi- 

 cated by the Earl of Rosse, K.P., &c. Received June 17. 



(Abstract.) 



In this paper an account is given of the observations which have been 

 made with the 3-feet and 6-feet telescopes on the great Nebula in 

 Orion during the last eighteen years. The observations are accom- 

 panied by an elaborate drawing. 



In the year 1852, Mr. Bindon Stoney made a drawing of the Huy- 



