488 Trans. Acad. Sci. of St. Louis. 
both prism and grating. The grating is 3% inch square, has 
17,296 lines to the inch and was ruled by Chapman on Ruther- 
ford’sengine. The clear aperture of the collimating and view 
telescopes is 1.4 inches, and their focal length is 15 inches. 
The view telescope is provided with a micrometer and an eye- 
piece which magnifies about 12 diameters. The slit is pro- 
vided with acomparison prism, and the jaws of the slit are of 
brass. 
The Transit Instrument is by Brunner of Paris and was 
made probably about 1850. The clear aperture of the tele- 
scope is 2.10 inches and its focal length is 23 inches. The 
spider-line reticule has five vertical threads about 3 seconds 
apart, and one horizontal thread. The illumination of the 
threads is effected by light which passes through a hole in one 
of the pivots and is reflected down the tube by a small mirror. 
The micrometer with which the instrument is provided is so 
constructed as to be practically useless. The diagonal eye- 
piece usually used was purchased of Fauth & Co. in 1891. 
Its power is 60 diameters, while that of the old one used until 
October 1, 1891, is 40. There is a reflecting cap for nadir 
observations. 
The levels which were furnished with the instrument by 
the maker are almost worthless for purposes of precision 
on account of irregularity in the bore of the tubes. The 
striding level is the better one of the two, but an investiga- 
tion made in June, 1890, showed that the average value of 
a division for one-half of the tube is 5”.4 and for the other 
half 3”.9. In April, 1891, these level tubes were- replaced 
by new ones of excellent quality made by Fauth & Co. The 
adopted value of one division of the new striding level is 
1”.869 + 0”.004, and that of one division of the new latitude 
level is 1”.01+ 0”.01. 
The pivots are 0.74 inches in diameter, and repeated trials 
with the new striding level fail to show either inequality in 
their size or irregularity in their form. The distance between 
the ends of the pivots is 11.4 inches. ‘The graduated circle 
in declination is 9.8 inches in diameter, is divided on silver to 
5 minutes and reads very accurately by two verniers to three 
Seconds of arc. 
