ASTRONOMY. 197 



Star charts, etc. — The series of ecliptic charts, by Dr. Peters, was 

 begun about ISGO, aud lias been continued and enlarged up to the pres- 

 ent time, and this work is still going on. It is intended to make a 

 series of charts, each of which shall include all the stars visible with 

 the 13-inch refractor of the Litchfield Observatory, in a certain region, 

 with their positions for 1800.0. As these charts are now about to be 

 published by Dr. Peters, some account of them may not be unwelcome. 



Instruments and methods employed. — The observations are all made 

 with the 13-inch refractor (made by Spencer). In the focus of this eye- 

 piece is a mica scale, divided into 100 parts, 50 on each side of Zero. 

 Each part is about 9".8, and for the more imi:)ortant stars half parts (or 

 decimals of a part) are read, so that their positions are known within 

 5", a quantity which corresponds on the scale of the charts to less than 

 inch 0.001, and hence to about the smallest quantity that can be conve- 

 niently plotted. 



On paper sheets about 17 x 14 inches are the lithographed blank 

 forms. Each map contains 20™ in Eight Ascension, aud 5° in Declina- 

 tion ; I"* additional in R. A. is added on each side (to i)reserve the star 

 configurations) as well as 10' in Dec. on each side. 



Each map thus contains 22™ in E. A. and 5° 20' in Dec, 2™ aud 20' 

 of which are in common with four other contiguous maps. 



One degree on these is 2.336 inches or 



]o = 2.330 inches. 

 1' =0.039 inches. 

 1" = 0.0007 inches. 



The process of constructing such a chart is briefly as follows : 



1. Having decided on the limits of the chart, all available catalogues 

 are consulted, and all stars within the limits of the i^roposed chart are 

 reduced to 1800.0, and entered in the chart in pencil and afterwards in 

 ink, keeping to Argelander's scale of magnitudes. 



2. Zones are then observed with the chronograph and mica scale. 

 The transits are observed over only one wire. 



These zones are about 15' wide in declination and as long in R. A. as 

 convenient, say 20™. Sometimes a zone 00™ long is observed in order 

 to obtain euough standard or determining stars. The right ascensions 

 are read to 0^1, the declinations to h parts (4".9). 



3. These observations are then reduced accurately to 1800.0, aud the 

 stars are pricked in with a needle-point through a ruled piece of oiled 

 paper. 



4. With the telescope (dark field) these star-positions are examined 

 aud a memorandum of the magnitude of each star is made. On the 

 next morning these zone stars are marked in ink according to the pencil 

 memoranda. As the catalogue stars are practically in Argelander's 

 scale of magnitudes, the whole of the catalogue and zone stars are 

 given on one scale. 



5. Many examinations and revisions with the telescox)e (dark field) 



