30 Mr. Bevan on certain Defects in the British Almanac. 



nomena observed by me are entirely inconsistent with this 

 supposition. If homogeneous light were used, then (on this 

 supposition) the bright-centred rings would disappear and 

 black-centred rings would succeed them as at the polarizing 

 angle of the glass. If white light were used, the rings in the 

 neighbourhood of the polarizing angle would be wholly co- 

 loured, and on changing the angle the intensity of the differ- 

 ent colours in each ring would alter, but there would be 

 nothing like contraction. Thus at a certain angle the bright- 

 est part of the red would be at the centre of the spot, and its 

 faintest part would be in the first ring; while for the blue the 

 places would be reversed : on increasing the angle the bright- 

 est parts of both would be in the first ring. Whereas in my 

 experiments there was no discoverable alteration in the co- 

 lours of the rings, there never was seen a bright red centre 

 surrounded by a bright blue ring; but the rings, without 

 changing their character as to colour, diminished steadily till 

 the central spot was as it were squeezed out. Whether the 

 only diamond which I have used may possess any peculiarity 

 which distinguishes it from those used by Sir David Brewster, 

 I cannot say. Meantime I may observe, that the singularity 

 in the reflexion at the surface of the diamond makes it not 

 improbable that there may be some singularity in the refrac- 

 tion also, and renders a more extended inquiry into the laws 

 both of its reflexion and of its refraction highly desirable. 

 Observatory, Feb. 16, 1832. G. B. AlRY. 



VII. On certain Defects in the British Almanac. By 

 B. Bevan, Esq. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 T S it not worthy of remark, that an Almanac published under 

 ■■■ the patronage of so learned a Society as that established 

 for the Diffusion of Useful Knowledge, should continue to 

 be published without giving the sun's declination? It cannot 

 surely be owing to a want of room, when two pages per month 

 are appropriated to the calendar. 



The patrons of this publication must be aware of the im- 

 portance of this information to all persons who may wish to 

 become acquainted with practical astronomy. The declination 

 of the sun is independent of the latitude of the place, and 

 therefore will serve for all the British dominions; whereas 

 the table of " sunrise" and " sunset" can be true only for the 

 particular latitude of the place for which it is calculated, and 

 can be of little, if any practical use; — at least, a general table for 



