SCIENTIFIC SUMMARY 
ASTRONOMY. 
FA YE and Mr. Stone on the Transit of Venvs in 1769. — At tlie Stance 
* de I’Acad^niie des Sciences, January 4, I8G9, M. Faye read a paper 
wliicli practically involved the assertion that Mr. Stone's re-discussion of 
the observations of the transit of Venus in 1769 was of little value, as 
having bjen anticipated by M. Powalky's treatment of the same subject. M. 
Powalky, it will be remembered, determined the solar parallax to be 8"*832, 
from a re-discussion of the transit of Venus, based upon more accurate de- 
terminations of the longitudes of the stations at which the several observa- 
tions were made. But it was objected to Powalky’s work that be rejected 
many observations at the more important stations for reasons which do not 
appear to be founded on any legitimate principles, and that besides employ- 
ing very few durations, those he actually employed are represented in so 
imperfect a manner in the residuals that very little weight can be attached 
to the result. It is to the hopeless task of giving importance to the results 
of Powalky’s labours, that M. Faye has set himself. We may, however, 
congratulate ourselves that he has done so, as Mr. Stone has been led, in the 
defence of his case, to give a very able exposition of the rules which should 
guide the mathematician in treating observations of a transit. In connection 
with the coming transits these rules are of the utmost importance. They 
are laid down as follows by Mr. Stone : — 
1. There were two phenomena of internal contact which were observed 
in 1769: the so-called real internal contact, and the apparent internal 
contact. These phenomena were, in the transit of 1769, separated roughly 
by about 16s. 
2. An observation of an apparent contact is not to be looked upon as an 
observation of a real contact, «nd vice versa. 
3. In any legitimately conducted investigation, the use of an apparent 
contact for a real contact, or vice versa, must lead to an erroneous value of 
solar parallax to the extent wliich an arbitrary change of about 16s. in the 
incongruous observation would affect the final result. 
4. If observations have to be rejected because of their incompatibility 
with the general run of the discussion, then every such rejection enormously 
increases the presumption against the truth of the investigation which re- 
quires such rejection. 
5. The absolute necessity of rejecting one good observation would, in 
