Progress of Astronomy during the Year 1879. 439 
gations of the velocity of light. From the experiments by 
Foucault, Cornu, and Michelson he deduces the most probable 
velocity of light =299,920 kilometers. Supposing the coefficient 
in the light-equation to be=498°3 (Delambre 493*2, v. Glasenapp 
500°8"), and combining this result with Professor Listing’s value 
of the equatoreal radius of the Earth, the solar parallax becomes 
= 8-802, while Struve’s constant of aberration combined with 
the velocity of light gives 8'"811. In conclusion Mr. Todd shows 
that if we combine the maximum value for the velocity of light 
with the maximum coefficient, and minimum velocity with 
minimum coefficient, r will lie between 878 and 8'"82, while 
the aberration in like manner gives the limits 8"°80 and 8'82. 
The American Congress has voted 5,000 dollars for apparatus 
to determine the velocity of light as accurately as possible. Pro- 
fessor Newcomb hopes in this way to find the distance of the 
sun with more accuracy than can be obtained by other methods, 
A new determination of the inclination of the ecliptic is con- 
tained in a doctor-dissertation by E. F. van de Sande Bakhuyzen, 
of the Leiden Observatory.* The author discusses the declina- 
tions of the Sun observed in Leiden in the years 1864-76, and 
enters into all details relating to the instrument used, &c. He 
finds that the inclination for 1870 as given in Leverrier’s tables 
should be diminished by about 0°30. This result agrees well 
with Oppolzer’s inclination for 1815 brought down to 1870, with 
a secular diminution as found by means of the latest values of the 
planetary masses. 
2. Theory of Instruments. 
Mr. Loewy has in the Comptes rendus (Vol. 87, No. 24) 
described a new apparatus for determining the flexure of a transit 
instrument. At the centre of the tube of the telescope is placed 
a concavo-convex lens from 1} to 3 inches diameter, and about an 
inch thick, the concavity being turned towards the eye-piece, and 
of a radius equal to the distance from the focal plane. A reflected 
image of a horizonal wire will in this way be formed by its side, 
and the flexure of the eye-end of the tube will be found as the 
tube is moved in zenith-distance. The convex surface is of such 
a radius that its focal length is one-fourth of that of the object 
* Bepaling van de Helling der Ecliptica. Leiden 1879, 8vo. 
