522 



Proceedings of the Royal Irish Academy, 



densation and apparent size of the nebulae (Astr. JTaclir., iN'os, 1463 

 and 1513), so that large and uncondensed nebulae gave the greatest 

 equation. But as the Athens obserrations are few in number, this 

 result could not be very reliable. I, therefore, thought it of interest 

 to see whether Schultz's comprehensive observations would show a 

 similar dependency, when compared with those of Schonfeld. The 

 result of my examination is found in the following two tables. As 

 might be expected, the condensation of a nebula has more influence 

 upon the estimation of the transits than its size. 



T-OIE I. 



NehulcE dassijied according to their apparent Size. 



Class. 



I. 



II. 



III. 



lY. 



Diameter of 

 Nebute. 



Aa cos S. 



Number of 

 Neb ulje. 



0'-2-0'-6 



-6 - 1 -0 



1 -5 -3-0 

 3 -0 -8 -5 



- 0^-28 

 -0-36 

 -0 -40 

 -0-46 



57 

 22 

 20 

 14 



Table II. 

 NelulcB classified according to the Degree of Co7idensation. 



Class. Appearance. 



Aa cos 5. 



Number of 

 Nebulae. 



I. 



II. 

 III. 



Planetary, or -sdth a 

 starlike nucleus, . 



Le3s condensed, more 

 irregular, . . 



Large & uncondensed; 



- 0^-15 



- -39 



- 0-44 



32 



53 



28 



"W^e have now come to the end of our researches about the- 

 different circumstances under which personal equations and errors 

 appear, and shall at last consider the probable origin of the pheno- 

 mena. 



III. 



"WTien Bessel had first remarked the considerable equation between 

 LimseK and his pupils, in the winter of 1820, he tried at once to explain 

 this remarkable phenomenon from the co-operation of the two senses, 

 sight and hearing, which takes place when an observation is made by 



