72 



magnetic force of the needles, as deduced from observations 

 of the previous year ; this may not he precise, and may 

 slightly change the number. The two needles gave respec- 

 tively : 



Bar. Cylinder. Diff. 



.9576 .9607 .0031 



" Taking your result for Dublin and London, and Captain 

 Sabine's for London and Paris, I deduce for the ratio of 

 Edinburgh and Paris, (the latter being unity) 0.8406, — which 

 is nearly identical with the direct comparison made by Pro- 

 fessor Forbes. It disagrees very materially with the result 

 of Captain Hall, by whom Edinburgh and London were first 

 compared ; but as the locality of his observations was shown 

 by Mr. Dunlop to have rendered them inaccurate, they can- 

 not be said to make against these determinations. I have 

 not yet had an opportunity to see how far Mr. Dunlop's 

 correction would make the three sets coincide. 

 " My determinations give : 



Philadelphia, . . . 1.0000 



Dublin, 0.8300 



Edinburgh, .... 0.7957 

 But, of course, the correction for the loss of magnetism 

 by the needle, if not exact, would affect these results more 

 than that for the two last named places." 



DONATIONS. 



Flora Batava, No. 109. By H. C. Van Hall. Presented 

 by the Author. 



A Copy of the Ordnance Survey of the County of Meath, 

 in 55 sheets. Presented by Lieutenant-Colonel Colby. 



On the Arenarius of Archimedes. By Stephen Peter 

 Rigaud, M.A., Savilian Professor of Astronomy, Oxford. 

 Presented by the Author. 



Mean Heights of the Barometer and Thermometer, with the 

 Fall of Rain, at the Observatory, Oxford, during each month 

 of the years 1828 to 1836. Presented by the same. 



