

Astronomical Society. 139 



series of observations upon this star, and at 11 hours found it of 

 the fifth magnitude, and equal to s and Lyras. Supposing the 

 period to be that assigned by Mr. Goodricke, eight revolutions 

 would have been performed in fifty-one days exactly; but when 

 viewed by Mr. Birt on the 12th of July, at 10 o'clock, it was about 

 3-4- magnitude, and less than y Lyrae; while on the 13th it was 

 decidedly of the fourth magnitude, and on the 14th of the third, or 

 as bright as y. Mr. Birt therefore concluded that it came to its 

 minimum brightness between the 12th and 13th, and that the 

 period was therefore longer than that assigned to it by Mr. Good- 

 ricke. This conclusion was confirmed by an observation on the 

 2nd of September, when, at 11 o'clock, the star was exactly equal 

 to e and , as on the 22nd of May, thus giving 103 days for sixteen 

 revolutions, or a period of 6 d 10 1 ' 40 m , instead of 102 days, which 

 would have been required if the period were 6 d 9 h . It would seem 

 that the duration of its maximum, as well as of its minimum bright- 

 ness, is somewhat irregular. Mr. B. gives several comparisons of 

 the star with y, e, and Lyrae, from May 22 to September 15. 



VI. A paper on terrestrial refraction, by the late Mr. Henry 

 Atkinson. 



On the fluctuations of the atmosphere near the earth's surface; and 



On the effect of such fluctuation upon the refraction at the 

 horizon, and at very low altitudes, especially on the dip of the hori- 

 zon at sea. 



(Unfortunately, these papers are unfinished: the ingenious author did 

 not live to complete them.} 



In these investigations Mr. A. proposed to himself to demonstrate, 



1st, The the fluctuations in the state of the atmosphere near the 

 surface of the earth are not only fully adequate to account for the 

 very great variations which have been observed in the horizontal 

 refraction, but even for still greater variations. 



2ndly, That the variations of the dip of the horizon at sea are 

 caused by the fluctuations of the atmosphere, and can be calculated 

 when the latter are known. 



The extreme uncertainty of the law of the variation of tempera- 

 ture near the earth's surface has been remarked by every observer 

 who has directed his inquiries to this subject, by a proper adapta- 

 tion of course and distance to the circumstances of the problem. 



We find well-recorded cases where small alterations of elevation 

 have produced very sensible effects upon the air, sometimes in- 

 creasing and sometimes diminishing its temperature ; and, again, 

 at other times, we find the temperature of the air nearly the same 

 through very considerable altitudes. (See Wells, Humboldt, &c.) 



In order to subject to calculation the different hypotheses which 

 may be imagined, Mr. A. supposes that the variations of tempera- 

 ture may be actually observed within certain limits of altitude (he 

 has here assumed fifty feet) ; and that the state of the atmosphere 

 at great elevations, for example at 1125 feet above the surface of 

 the earth, may be considered to be in a mean state. Considering 

 the state of these upper and lower portions of the atmosphere to 



T 2 remain 



