October 8, 1908] 



NA TURE 



57- 



with a hill 2° high the azimuth is verv nearly 

 N. 54^^ E. 



Q 



H 

 < 



the solstices and in May and November, the 

 changes in azimuth caused by varying heights of the 

 horizon being' also indicated. 

 These diagrams are gooel 

 for the whole of Britain and 

 for part of Brittany. They 

 have been computed by Mr. 

 Rolston, of the Solar Physics 

 Observatory. 



There is a relation between 

 the height of the horizon and 

 the refraction correction which 

 may be found useful. If the 

 horizon is half a degree high, 

 the refraction is practicallv 

 compensated, as the following 

 table will show : — 



Elevation of Bessel's Combined 



actual horizon refraction effect 



55 56 57 58 59 60 61 62 63 64 65 66 67 



Fig. 23. — .\zimuths of the May Sunrise. Sun s declination i6' 20' N. 



The above diagrams show very plainly the great 

 variation in azimuth the archaeologist has to reckon 

 with when he 

 roams Britain 

 t o determine 

 the orientation 

 of his monu- 

 ments, whether 

 ou t s t a n ding 

 stone, recum- 

 bent stone, 

 avenue or crom- 

 lech. What hap- 

 pens with the 

 solstitial sun 

 also happens 

 with the May 

 and November 

 suns, and 

 warning- and 

 clock - stars. 

 Thus we find, 

 in the case of 

 the summer 

 solstice sunrise, 

 it is seen, with 

 a sea horizon, 

 in az. N. 37° 

 E. at Stenness 

 and N. 50° 30' 

 E. in Cornwall. 

 K hill ii° high 

 in lat. 59° 

 changes 37° to 

 4ii°; a hill 2° 

 high in lat. 50° 

 changes 505° 



In the absence of measure- 

 ments, it is convenient, there- 

 fore, to assume, in the first in- 

 stance, that the height of the 

 horizon is half a degree ; then no refraction correc- 

 tion need be applied. 



Q 

 D 

 H 



into 54°. 



Having now 

 indicated the 

 importance of 



the measurement of altitude as well as of azimuth, 1 

 give diagrams showing the azimuths of the sunrises at 



NO. 2032, VOL. 78] 



FlG.'24.- Azimuths of the November Sunrise Sun's declination l6' 20' S. 



This relation is utilised in the preparation of general 

 tables and curves, as it provides us with a convenient 



