to an Astronomical Clock and Telegraph Register. 215 



sockets^ Two turns of a screw might elevate; one turn more 

 reverse it, and two more turns place it at rest on the socket and 

 friction rollers. 



The net work of the transit instrument may consist of groups 

 of five wires, each separated by an interval of once and a half 

 the ordinary space. 



For the sake of rapid observation of circumpolar stars, , the 

 inner group may have half the ordinary interval. In the case of 

 equatorial stars, only three of these wires need be used. The 

 equatorial intervals may be on§ for the inner, and two seconds 

 for the other groups. The intervals between the groups may be 

 three seconds. My micrometric measures, with the great Fraun- 

 I hofer equatorial s, show that fifteen-hundredths is an ordinary, 



[ and two-tenths of a second of time an extreme value of the sub- 



tense of a spider line for a four foot tube. The smallest clear in- 

 tervals between the wires would be four, the ordinary nine, and 

 the greatest fourteen, diameters of the opake wires. 



The number of these tallies may be seven, nine, or eleven, ac- 

 cording to the focal length of the telescope, and the mechanical 

 facility of graduating the diaphragm and of setting the spider 

 lines. Since the register is permanent, and may remain for refer- 

 ence, it is only necessary to enter in the written journal the mean 

 for each tally from the mean of the five readings. Tc prevent 

 the accumulation of these registers from filling too much space, 

 the same fillet of paper may have several parallel lines of the 

 automatic clock registers imprinted on it, by means of a microm- 

 eter motion of the graver. 



Where the observatory is fixed, and the line short, and the 

 Grove's cups are charged anew with acid every day, the register- 

 ing fillet may contain one or two months" continuous record on 

 one reel. All the transits observed in the occupancy of a single 

 temporary station may be preserved on one reel. In order to iden- 

 tify dates, and particularize records, the observer keeps a memo- 

 randum book in which he records the level readings, and refers to 

 each celestial object by a letter or number, with accents or side 

 numbers denoting the order of the lines on the fillet. 



A duplicate mark is made on the fillet itself. A receiving reel 

 °f dimensions similar to the delivering one, affords a compact dis- 

 position of the printed register. A tell-tale check connected with 

 " will enable the transcribing clerk to turn at once to any date 

 on the paper, without examining the intermediate spaces. 



In using these instruments for longitude operations, zenith stars 

 are selected at the eastern station. The declination clamp is ad- 

 justed ready for reversals. 



The levels are all read. Twenty dates of bisections in the first 

 position of the instrument are imprinted, the reversal and re-point- 

 * U S is effected, twenty more bisections by the same wires in a 



