OCR Text |
Show 15 Western Union Telegraph Company were brought into the tent by a loop. By means of automatic repeaters the signals were sent to the connected stations- the repeaters being placed at Oorinne, Cheyenne, Omaha, Chicago, Pittsburgh, and Philadelphia. In relation to the personal equation, I have to state that, as far as it is known in this office, this value for the relative error of the observers has not been determined. Mr. Austin was in Washington in the spring of 1873 for this purpose, but no satisfactory results were obtained. The resulting longitude is therefore affected by this relative error. OBSERVATIONS TO DETERMINE THE CLOCK- CORRECTION AT THE UNITED STATES NAVAL OBSERVATORY. The instrument used in these observations is that known as the u meridian transit," which has been employed at the Observatory for many years, and is now situated in the east wing of the building. The description of this instrument may be found in the " Washington Astronomical and Meteorological Observations" for 1862. The transit was employed in 1871, under the direction of Prof. M. Varnall, United States Navy, in observing stars for the " General Catalogue f and, as the observations for time used in the longitude work were made after the regular work with the instrument was finished for the night, the same observations for collimation were employed in reducing the time- stars as were used in the reduction of the regular work. The system of transit- threads in this instrument is composed of five groups or sets. When the clamp end of the axis is east, the set which is first reached by a star in its transit at the upper culmination is known as set A, and the others as sets B, C, D, and E. During the early part of 1871 the equatorial interval between each thread in the five sets and the mean of B, C, and D was found to be » follows: Thread. A, A! t *! Interval 37* 897 35.972 34.308 32.745 3a 205 Thread. £:::::: Interval. 9. 19. 8) 6 17.563 15.069 I Thread. C, g » 8;:::::: Interval. 3.183 1.654 9.014 1.639 a 231 Thread. ft 5* Interval. *• 15.146 17.589 19.110 Thread. B4 E, Interval. 30.003 32.647 34.153 35.820 37.693 The reduction for G3 is + 0*. 014 when the clamp end of the axis is cast The clock used is that known as the " mural clock," and is mounted against a stone pier in the transit- room. It is connected with the chronograph in the usual way, and closes the circuit at each second, except at the sixtieth second of each minute, when a small ivory lever on the axis of the escapement- wheel raises a very delicate spring, which forms a portion of the circuit, and prevents the closing of the circuit at that instant. The observations of all except circumpolar stars were recorded in the usual manner by the chronograph, which is described in the annual volume for 1862. in the reductions, whenever a broken set of observations occurred, each thread was reduced separately. Instrumental corrections.- The corrections to the observed transit of a star were derived from the observed and computed errors c', n', and m'. The error of collimation is represented by &\ the equatorial value of |