310 THE PRESIDENT'S ADDRESS. 



the variation in the length of a degree perpendicular to the 

 meridian. The longitudes are all in defect about 3^ part of the 

 distance of the station east or west of Greenwich, and are there- 

 fore, for scientific purposes, practically obsolete. Taking one 

 illustration of the effect of this error, I find it stated in Vol. I, 

 p. 15, of Davies Gilbert's " Parochial History of Cornwall," 

 that " St. Agnes Beacon was chosen as one of the principal 

 western stations in the great Trigonometrical Survey of England. 

 The position of the summit was then determined with great 

 accuracy: latitude, 50° 18' 27" ; longitude, 5° 11' 55-7". In 

 time, 20m. 47-7s." When this erroneous longitude of St. Agnes 

 Beacon is corrected, by adding -^ part, it becomes 5° 12' 58-1" 

 or in time, 20m. 51 -9s, as it is now correctly given in the more 

 recent editions of the Ordnance maps. The true geographical 

 position of this important station is therefore about 4,050 feet 

 farther west of Greenwich than that assigned to it in all the 

 Cornish historical or descriptive works that I have seen. The 

 same remark applies, more or less, to all the longitudes of the 

 other stations of the Ordnance Survey in Cornwall, taken from 

 the erroneous table published in 1800. 



While preparing these notes, I have been encouraged to 

 deviate, in some measure, from the strictly local character of 

 most of the addresses of my predecessors, by the important 

 remark of a past-President of the Institution, that "astronomy, 

 perhaps, has not hitherto received from us the attention it 

 deserves."* I have, therefore, taken for granted that you are 

 expecting from me some account of recent researches connected 

 with that popular science, of which I have been an active student 

 since I joined the staff at the Poyal Observatory in 1838. I do 

 not, however, intend to read to you a long sensational essay on 

 the romance of astronomy, for I presume you are already familiar 

 with many of the wonders of the starry heavens ; as I prefer to 

 occupy your attention by saying a few words on a far more diffi- 

 cult subject, and one probably new to many now present, 

 relating to the physical constitution of the heavenly bodies, as 

 determined from recent researches on the analysis of the light 

 emitted from their gaseous photospheres. I shall also briefly 

 describe to you a few of the marvellous photographic delinea- 



* Journal, E.I.C, Vol. ix, p. 383, 



