OP THE EXPEDITION. XXXIX 



months. The winter of 1850 had convinced me that with so small a corps it would be impossi- 

 ble to sweep all the space between our zenith and pole, and I had limited the upper zone at 

 declination 65 50'. As soon as the map was filled, showing that all the space south of that 

 parallel had been once swept, they employed the remaining nights in re-observing doubtful 

 spaces when individual measurements or magnitudes were marked for such revision each of 

 them not unfrequently making a series on the same night. Winter as it was, on 57 nights, 

 between May 29th and September 9th, above 5,000 stars were observed, clouds obscuring those 

 remaining of the preconcerted term. Too much praise cannot be given these gentlemen for the 

 capability, zeal, and assiduity manifested in the laborious duties undertaken. Trials of patience 

 and hours of physical discomfort were inevitable concomitants of zone work with our circle, yet 

 there was no abbreviation of tasks partially self-imposed, and I boldly assert that few have ever 

 persevered more cheerfully under the continuous employment which unfavorable weather forced 

 on some months of our stay in Chile. 



The observations for longitude, though not very numerous, probably give a very near approxi- 

 mation to the truth. There was no leisure to compute anticipated occupations for ourselves, 

 and the Nautical Almanac tables were not reliable. Moreover, neither the zone work nor the 

 differentials with Mars and Venus could be interrupted for the observation of occultations or 

 moon-culminations. When the latter were not interfered with, every star predicted in the 

 almanac as liable to occultation was looked for at the proper time ; but there was more than 

 one occasion when no occultation occurred, although the ephemeris made it nearly central in 

 that parallel, and thus the list embraces only forty-four occultations one hundred and seven- 

 teen moon-culminations. On the 5th of January, 1852, there was witnessed the very rare occur- 

 rence of a double occultation of t Geminorum. There are several lofty mountains with deep 

 intervening valleys on the southern hemisphere of the moon. These become very conspicuous 

 when the moon is far north, and in our note-books it was essential to record whether the zenith 

 distance of the summits or that of the circular line of the disc was observed. On this occa- 

 sion,, i Geminorum remained 2m. 36.4s. behind the first mountain, was 36.9s. traversing the 

 valley between ^t and the proximate peak, and finally emerged 4m. 05.8s. after the first dis- 

 appearance. 



The first contact of the moon's limb with the sun at the solar eclipse June 17, 1852, was hid- 

 den from us by clouds ; but as the differences of their diameters were measured at transit over 

 the meridian, and the end of the phenomenon was observed, these will add to the reliable data 

 bearing on the determination of our longitude. 



The meridional distance between the observatory on Santa Lucia and that of Mr. Mcuatt, in 

 Valparaiso, was ascertained by exchanging telegraphic signals, for which purpose the operators 

 kindly placed the line at my disposal a few nights before I finally embarked from Valparaiso. 

 Every precaution was taken by Lieut. MacEae at Santiago, and myself at Valparaiso, to insure 

 an accurate result, and the mean of 100 signals 50 each way showed the difference of longi- 

 tude to be ?>m. 56.51s., with a probable error of i 0.021s. 



For the reason respecting occultations and moon-culminations given in the preceding para- 

 graph, meridian planetary observations, except of Mars and Venus, are also few in number. 

 Neptune, the planet to whose orbit our late able countryman Prof. S. C. Walker had devoted so 

 much labor with such distinguished success, was followed at opposition whenever the zones 

 would permit ; but this was the only one. 



A complete set of portable magnetical instruments was made under the direction of Colonel 

 Sabine, K. A., by Jones and Barrow, of London. This embraced a declinometer, a unifilar 

 magnetometer, with a separate vibration apparatus and a dip-circle, with reading microscopes, 

 all which instruments are described in a volume by Captain Riddle, R. A., published by 

 authority of the Lords Commissioners of the Admiralty, and are noticed more at length in the 

 appropriate volume (Vol. fi) of our work. Finding that the rock of Santa Lucia strongly influ- 

 enced the magnets, as the iron bars of our windows wen 1 too near for absolute determinations 



