486 THIRD REPORT 1833. 



cotidal lines (or lines along which it is high water at the same 

 instant,) will be discovered. It would be very desirable for 

 those who have the opportunity, to combine so as to effect the 

 detailed description of the tides through some small extent of 

 coast, such as that which has been effected by M. Daussy for 

 the west coast of France. 



AURORA BOREALIS. 



Notwithstanding the attention which has been paid to the 

 phaenomena of the Aurora Borealis, and the various hypotheses 

 which have been imagined to explain them, it will be found 

 that there is a want of information on the points which are 

 most necessary as bases of induction ; and the British Asso- 

 ciation have therefore been induced to appoint a Committee in 

 the express view of directing observers to the really important 

 features of this meteor, and of obtaining, by a system of con- 

 temporaneous observation, data which experience shows cannot 

 be derived from insulated exertion. 



The following are the most important points which demand 

 the attention of observers: 



1. The elevation of the auroral arches and streamers above 

 the surface of the earth. 



2. The determination of the question whether the auroral 

 exhibition is accompanied by sound. 



3. The existence of recurring periods of frequency and bril- 

 liancy in the Aurora. 



4. The influence of arches, streamers, and other aui'oral 

 phaenomena upon the magnetic needle. 



1 .) It is recommended to all who intend to observe Auroras, 

 to make themselves well acquainted with the names of all the 

 principal stars to the north of the equator, especially those 

 which do not set here. This will be most easily done by stu- 

 dying a celestial globe. Good maps of the stars may also be 

 consulted with advantage. Either the proper names or the 

 Greek characters with the name of the constellation will be 

 sufficient. 



Persons who may prefer to determine the angular elevation 

 and position of the arches and streamers by graduated instru- 

 ments, must be supposed well accustomed to the use of them ; 

 they may, however, be reminded, that telescopic sights are 

 for this purpose useless, and that steady instruments, which 

 can be handled with ease and expedition, are much more avail- 



