The sun. [volume] (New York [N.Y.]) 1833-1916, 1902-01-05
SCIENCE.
DIMENSIONS AND MASS OF MERCURY

be Interesting to repeat them by means u
one Of the double image micromcter' Of The
observatory Many Observers. the present
writer for one, have doubts whether hlar
~micrOmoters arc oapaul" Of giving &C.
curate results for planetary diameters. Con-
~si,tnucy In such measures Is no proof 4
accuracy DR. Lee remarks Of the ply
seal appearance Of th" planet that. there
in approaching the planets border. ard
that the observer gets the Impression thyt
the physical condition of Mercury IL r"ry
similar TO that OF our noon from a, d.
cussion Of various observation, he concludes
That the c1rth j. the most dense planet, IN
the solar System. Venus the next. and that
The density of Mercury is To that OF the earth
Ia the proportion Of 80 to 80.
DENSITY y FIGURE or CLOSE BINARY STARS.
stellar statistics based on observations at
the Lick University show that one star In
five or six. Is a spectrosCoric binary. We
may estimate, therefore,. that there are about
500 variables Of the type Of AtOoi brighter
than the ninth magnitude. though only
twenty-five such systems are now known.
From known formula il has been calculated
by Prof Russell Of Princeton that the mean
density of II AlEol stars il OLE water being
taken rs unit density. -Four southern Algol
vsriablcs give thg, same density. and eight
others give DIS. This close agreement is not
likely to be fOrtuitou- AID the density In
dicatcd Is such Us would favor the disruption
OF a rspidly rotating ms obseryatio1s
u'''l q ~ WIZ - u
would determine the tgur" of the two COM
pouents Five Of tn" Alg stars revolye
comynnents Of two others arc known to be
ollipsoid another R r. Coutauril Is prob
2hiy Of ne h1ps Of one 81 pIoi Par VIM
certain cases then the shapes. OF the com-
poncnt starr OF a certain class OF btnaries have
been made out To appreciate the advance
consider what CopcrHICUs or kcpler or even
l|pltce would say to an announcement OF
the sort.
L1HEH AND GRAv1TATtoHAL NATTER HhoUo
INDEFINITE SPACE.
Lord Kelvin has the following remarks
on the hypothesis that IL we could see far
enough into space the whole sky would
covered with stars, all OF about the
the same brightness as our sun, and that
the reason WHY the whole sky is not thus
illuminated Is that starlight Is absorbed
by the ether In It's journey through space.
He says:
Now we have our irrefra gable dynamics
proving that the whole life OF our sun asa
IS a very moderate number Of MIL
lion of years, probably less than 5),0o0.00,
between 80 100000 and iQO.Oo0.0o0
Thus tho time taken by Light to travel from
he outlying stars OF our sphere 70 t,e
Of a star. Hence II all the stars through our
vast sphere commenced shining at the same
time. 3.ej .ODn times the life of a star would
Inr the earth from the outlying stars. and at
no one. instant would light be reaching the
proportion OF all the stars. To make the whole
sky nglow with the light Of all the stars at the
must be timed earlier and earlier for
he moro md more distant ones. so that
he time Of arrival Of the light Of every one
u those al tn" earth may fall within the
1urations Of the ligths al the earth OF all
he others.
RADIOACTIVE LEAD SALTS.
Holman snd Strauss have obtained radio
ictive salts o. lead from various rare minerals.
he radioactive lead differs in many respects
rom ordinary lead In It's chemical behavior.
but it has not yet been obtained in its pure
.tute. All the various salts have a similar
upon the electroscope. but only the
is capable OF acting upon a photo
plate through glass or aluminium;
the sulphate becomes particularly
IN the latter respect efter having BEEN
by iI'ric and sulphurio acids or
.f'cr having been ignit"d a. $50 for is hours
Vile radio-active lead s~uiphnte acts more
'r'rRotCally on e photographic plate thgu
rer arafiOr tho latter have = much greater
c'ion h. tlscharr,Is The eiectrcscop"
hororrarhic means ar" not Identical with
hose thu' produce electric discharges.
or THE ULTRAVIOLET RAYS.
The great inter .'y Of the light effects
reduced by an electric spark has led H..
.reuslor TO e1 experiment. with "a view 10 deter
20 a new method IN photomrtry The
FOR the spark v.r" ALUMINIUM.
d 70. ar alloy Of 2irc 49, cadmium. &c, II
,l,C' r..os W'r" ~ 'hc same metal no
1r .'Hr' lIgl' was oH'ti.r1 IN the case Of
!gri.g" ltts co s'l'ry was, however.
t'.rrai vhe' 'NH r~uEIflN" pole was n, that
r,tIL. AID the method seems promising
E~ErEoprlrIoss OF MAPS ASD
HuAH.HtLa