ASTRONOMY AND BAROMETRIC HYPSOMETRY. 545 



nometers, to have deduced the longitude of some elevated point from occul- 

 tations alone ; but, unfortunately, the only two good occultations which 

 occurred during our presence in the Hills, viz, a Scorpii, on June 16, and 

 a Virginia, on August 6, were both lost. The first occurred while we were 

 at Camp Harney, a place almost exactly on the meridian of Harney Peak, 

 and after making very correct observations for the local sidereal time and 

 getting my telescope in position, I had the mortification to see the moon 

 sink behind the western slope of Lookout Mountain Jive minutes before the 

 occultation took place. The second was lost by the failure of our ambu- 

 lance containing my telescope to meet us at our appointed rendezvous. 

 Both of these stars were of the first magnitude and disappeared behind the 

 dark limb of the moon. The loss of these occultations was disheartening 

 to me in the extreme, as they would have enabled me to have fixed our 

 positions within a mile. 



Observers in the field do not place that degree of confidence in longi- 

 tudes obtained from occultations, to which I think them entitled; and from 

 my long experience I am led to believe that the indifferent results generally 

 found from observations made in the field are greatly owing to the want of 

 experience in the observers themselves, and to errors in the exact local time. 

 With a 2-inch telescope, or that of a theodolite, stars as small as the third 

 magnitude will be easily seen close to the dark limb of the moon, when she 

 is not more than five days old. A single observation of an immersion by 

 a practiced observer, under the above conditions, will give the longitude to 

 within three seconds of time, and in this statement I have the concurrence 

 of some of the most eminent astronomers in the country. 



The longitudes.of the more prominent peaks in the Black Hills deduced 

 from my chain of "meridian distances" agree very nearly with those of 

 Captain (now General) Gr. K. Warren, who explored the western, southern, 

 and eastern portion of the hills in 1857. His longitudes were, I believe, 

 determined b}^ moon culminations, which, next to occultations, is the safest 

 and surest way of determining absolute longitudes, when the base or prime 

 meridian is very far distant. From our triangulations the relative positions 

 of Bear Butte, Dodge Peak, Custer Peak, Crow Peak, Terry Peak, 

 Inyan Kara, Warren Peaks, and Bear Lodge are correctly located with 

 35 B H 



