254 



Mr. J. A. Broun on the Annual 



[Mar. 26, 



of translation in the visual direction of some portions of the nebulous 

 matter within the nebula, which might be found by comparing the 

 different parts of a large and bright nebula. 



Sir "William lierschel states that " nebula were generally detected in 

 certain directions rather than in others, that the spaces preceding them 

 were generally quite depriA^ed of stars, that the nebulae appeared some 

 time after among stars of a certain considerable size and but seldom 

 among very small stars, that when I came to one nebula I found several 

 more in the same neighbourhood, and afterwards a considerable time 

 passed before I came to another parcel"*. 



Since the existence of real nebulas has been established by the use of 

 the spectroscope, Mr. Proctorf and Professor D'ArrestJ have called 

 attention to the relation of position which the gaseous nebulae hold to the 

 Milky Way and the sidereal system. 



It was with the hope of adding to our information on this point that 

 these observations of the motions of the nebulae were undertaken. 



In the following list the numbers are taken from Sir J. Herschel's 

 ' General Catalogue of Nebulas.' The earth's motion given is the mean 

 of the motions of the different days of observation. 



III. "On the Annual Variation of the Magnetic Declination." By 

 J. A. BROUN, F.R.S. Received February 11, 1874. 



The first observations which seemed to show that the mean position 

 of the declination-needle followed an annual law were those of Cassini, 

 made, more than eighty years ago, in the hall of the Paris Observatory 

 and in the caves below it (90 feet under ground). It cannot be said, 

 however,- that Cassini's result has been confirmed by subsequent observa- 

 tions, either as regards the direction or amounts of movement from 

 month to month. 



The extensive series of observations made in different parts of the 



* Philosophical Transactions, 1784, p. 448. 



t Other Worlds than Ours, pp. 280-290. 



J Astronomische Nachrichten, No. 1908, p, 190. 



