6 o 
Mr. Pond on the parallax of a Lyra. 
have produced, on my mind, a conviction approaching to 
moral certainty. The history of annual parallax appears to 
me to be this : in proportion as instruments have been im- 
perfect in their construction, they have misled observers 
into the belief of the existence of sensible parallax. This 
has happened in Italy to astronomers of the very first repu- 
tation. The Dublin instrument is superior to any of a simi- 
lar construction on the Continent; and accordingly, it shows 
a much less parallax than the Italian astronomers imagined 
they had detected. Conceiving that I have established, beyond 
a doubt, that the Greenwich instrument approaches still nearer 
to perfection, I can come to no other conclusion than that this 
is the reason why it discovers no parallax at all. 
