UNITED STATES ENGINEER OFFICE, 

 GEOGRAPHICAL AND GEOLOGICAL EXPLORATIONS AND SURVEYS 



WEST OF THE IOOTH MERIDIAN, May i, 1873. 



Memorandum of istructions for conducting observations for longitude and latitude at a main or primary astronomical station 



for the field-season of 1873. 



The fixed observatory, with which connection will be made, is in Temple Square, 

 Salt Lake City, Utah, and in charge of Assistant John H. Clark. Every observer is 

 responsible for the receiving of the signals from the connecting-stations for certain re- 

 ductions of results, as full as possible, and will follow such other instructions that may, 

 from time to time, be given. This station will be changed during the season, probably 

 in the month of August, to the United States engineer observatory, to be constructed 

 at Ogden, Utah. 



i. Observations for Longitude. 



In carrying on the astronomical campaign, preference will be given to the longi- 

 tude-results for those nights that are clear at both stations; that is, the observers in 

 charge, after having completed the necessary arrangements for the observations and 

 exchange of signals, will, from this time on, exchange signals each night that shall be 

 fair at the two stations, unless unavoidable difficulties arise to prevent. 



It will be carefully observed that weather-signals are sent by telegraph each 

 evening about 6 p. m. while the exchanges are going on and until the full series at 

 a station shall have been completed. In case of uncertainty as to the possibility for 

 observing for anyone night, this ma}' be indicated in the first dispatch; and subsequent 

 dispatch or dispatches, between this time and 10 p. m., shall determine whether 

 exchanges shall be made that night or not. 



Some convenient and concise form will be adopted for the weather-signals, and 

 in no case must there be a failure as regards forwarding them. 



It may be admissible, contingent upon the stage of the prosecution of the work, 

 should the weather at Salt Lake at about 6 p. m. look unfavorable, that the observer 

 at the distant station should at once conclude to take that night for latitude-work, 

 which may be done after informing the observer at the Salt Lake or the receiving 

 station. 



For the conducting of the observations for the exchanges for a single night, the 

 following instructions will be adhered to: The transit of stars for time-determinations, 

 consisting of not less than three time and two circumpolar stars in each position 

 of the instrument, both before and after the transmission of the signals, will be taken. 

 Of course, should the night be sufficiently clear, so that it seems possible to make the 

 time-determinations at both stations, by the modification of the above, so that at 

 one or both of the stations the transits of stars may be made entirely before or 

 entirely after the sending of the signals, the strict following-out of the above is not 

 necessary. 



These instructions are made with the understanding that a twenty-six or thirty- 



