New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1895-10-07

posed to haunt interplanatory space. Thence the
elaborate attempts made thus far TO obtain ac-
curate measurements have been confined to the
very largest of the collection and especially the
four first discovered Sir William Herschel esti-
mated the diameter of vesta dong considered the
largesD about $50 miles that OF Ceres 1872 Pallas
l47 and Juno still less. Professor Pickering. OF
Harvard. made Vesta's diameter $40 miles, and
computed the other three nearly alike and about
two-thirds the size Of Vesta.
The general plan pursued in nearly al! this work
was, however, open to serious objections 1t was
based on the relative brightness OF the bodies
measured. But II Is known that the major planets
vary among themselves greatly in their power Of
rejecting the suns light, and 1t was impossible to
say whether the asteroids possessed the albedo'
OF Venus To which Muller gives the highest re-
fectlng capacity. OF Mercury which. area for
area, throws back only about one-sixth as much
light as his lovely sister. Again, how could one
tell whether the asteroids all had the same albedo?
L is now found by Professor Barnard that they
haven't; and that Vesta generally credited win win
thing better than the photometric method has
fore. ana OF late years efforts have been made
with small telescopes to use the micrometer an In
strument with a scale inserted crosswse in the
telescope eyepiece and employed In ascertaining
the distance between neighborins stars and The
in the telescope than the minor planets DO. These
latter We're 80 very small as 10 defy m.crometric
examination for long time. But the great LICK
telescope. with 1t. unequalled magnifying power
afforded exceptional opportunity Tor measure
ment by what Is regarded the most trusty plan,
and Professor Barnard has been utilizing II system
atlcally and repeatedly so as 10 accumulate
sufficiently large number OF measurements 10 give
him an average In which confidence could be re-
posed This exceedingly delicate and fascinating
task has now been carried so far that he feels
willing to give his figures TO the world.
These are as follows: Ceres, M miles, Pallas.
3oi: June. il8 and vesta 2iS Compared with the
earth's satellite (Which Is .. 1853 miles In diameter
according to Young) these planets would look
about as the small circles numbered l. 2, and 4
in the diagram do beside the larger But
the asteroids are several hundred times distant
from US as the moon, OF course this proportion
does not hold good In actual observation The rea-
tive rejecting power Of the hour. compared with
Mars which Is placed at !, Is computed by Bar
nard as follows: Ceres. 0s7; palas. 0S; Juno l6T
and Vesta 2C7. The remarkable brightness OF the
one last named. four times that OF Ceres. explains
why Vesta long believed 10 he the largest
Similarly IL H. now easy 10 see why the tiny Juno,
very much smaller than Ceres aud Palas was
ranked : their equals
The type OF mcrOmeter used In measuring pian
somewhat resembles that illustrated herewith, but
ia 50 modified as TO give n double image In order
10 get rid o, certain misleading optlcal phe-
nome non called "irrsdiatlon." by bringing the two
disks into contact that embarrassment disappears.
The measurement is then made, by the scale in
seconds OF an arc and fractions OF a second from
which and from the distance OF the object the
diameter 10 then computed