Friedrich Wilhelm August Argelander. 113 
as seen in the microscopes than the spider lines, by means of 
which the bisections are made. The advantages of this system 
are obvious, viz: perfection of surface permitting a line of any 
desired fineness—facility of illumination permitting the exten- 
sion of the power of the reading microscopes to several hun- 
dred times—smallness of dimensions and consequent cheapness 
and avoidance of almost all the questions of flexure and loca 
effects of temperature. 
I am convinced from the ease with which one second is 
read on my instrument, with microscopes only 42 inches 
long including objectives and eye-pieces, that upon a circle 
of fifteen inches provided with powerful microscopes, greater 
precision could be attained in the reading of angles than with 
the largest metallic circles now in use. 
or the purpose of showing the degree of precision attain- 
able, I add two series of bisections of lines on the circle made 
A a and two made by a lady, marked respectively R. 
n . 
R. M. M. 
aa 1'"8 23'"6 ii" 
7 *4 1 3 23 °6 11 ‘2 
fie 19 23 3 11 °8 
7 °4 1 °8 23 °8 11° 
7°38 1 *8 24 '5 10 9 
7 °6 rs 23 -9 Lies 
boa | +o 23 °7 11 5 
7 °4 Q- 94° bis 
7 6 23 23 °9 1i-° 
7 °8 2 °3 24-3 11 °4 
Mean, 7'-54 1'"89 23'"-86 11-28 
Tt will be readily seen that the probable error of any single 
reading in any one of these series is considerably less than half a 
Second, while the probable error of the mean of any series is a 
much smaller fraction. 
New York, June 1, 1876. 
SS 
Arr. XVIL—Friedrich Wilhelm August Argelander.* 
ye eeRICH WitneLm Avueust ARGELANDER was born at 
emel, in East Prussia, on the 22d March, 1799. His father, 
Was of Finnish descent, was a merchant of that town, whilst 
agai belonged toa German family. Their circumstances 
a as enabled them to give their son a very careful 
schenetice is principally an abstract of that by Prof. Schénfeld in Viertel- 
from the « der Astronomischen Gesellschaft, Jahrgang x, part 3, and is here cited 
Monthly Notices” of the Astronomical Society. 
