532 



The Astronomer Royal on the Circularity 



Intensity of the compared 

 currents. 



tan 0. 

 tanfl' 



Formulie of correction. 



Errors committed, in 

 per cents. 



Stoncy. 



Zengcr. 



Stoncy. 



Zenger. 



1: 2 



0-500C0 



0-86029 



067236 



0-58750 



per cent. 

 345 



per cent. 

 11-8 



1: 3 



0-33333 



072750 



0-38854 



0-38273 



16-6 



148 



1 : 4 



025000 



0-65335 



0-31520 



0-27075 



261 



8-3 



1: 5 



0-20000 



0-60523 



0-25120 



0-21994 



25-6 



100 



1: 6 



016667 



057677 



0-22136 



019319 



328 



159 



1 : 7 



014286 



0-54208 



018846 



16365 



281 



146 



1: 8 



012500 



051819 



016765 



014522 



341 



16-2 



1: 9 



011111 



0-49695 



0-15074 



013010 



357 



171 



1:10 



010000 



0-47412 



013394 



11482 



339 



14-8 









Average 



2969 

 2-165 



: 1372 

 : 1 



The errors arising from the use of Mr. Johnstone Stoney's 

 formula considerably exceed those arising from the use of my 

 own formula. No doubt these numbers prove the advantages of 

 this formula, and they suffice to show distinctly that, in conduct- 

 ing investigations in which accuracy is a point of importance, 

 Mr. Johnstone Stoney's formula cannot be used. 



Vienna, January 8, 1862. 



LXIX. On the Circularity of the Sun's Disc. 

 By G. B. Airy, Esq., Astronomer Royal*. 



IT has been proposed lately to prepare an apparatus for the 

 purpose of examining whether the Sun's disc is really cir- 

 cular, and in particular for ascertaining whether the diameters 

 nearly perpendicular to the ecliptic are equal to those nearly 

 parallel to the ecliptic. I would not by any means discourage 

 the trial of such apparatus ; but I would unhesitatingly express 

 my opinion that the result of the trial would be to show whether 

 the apparatus is or is not trustworthy, and not to give any new 

 information regarding the measure of the Sun's diameters in any 

 degree comparable to that which we already possess. 



Perhaps few persons except professional astronomers are aware 

 of the enormous amount of evidence which already exists in refer- 

 ence to the values of the Sun's diameters, and of the way in 

 which this evidence is growing every day in the ordinary routine 

 of meridional observations. To make this fully understood, I 

 will here explain what is prepared in the Nautical Almanac, what 

 is observed at the lloyal Observatory, how the observations are 



* From the Monthly Notices of the Royal Astronomical Society, Janu- 

 ary 10, 1862. 



