550 Royal Society. 



The observations I propose to make are, — Mars on the meridian 

 and extra-meridian, during the oppositions of 1849 and 1852; and 

 Venus under analogous conditions at the inferior conjunctions and 

 stationary terms of 1850 and 1852. These observations will be dif- 

 ferential, and (as the grant of congress implies) are the paramount 

 objects of the expedition ; but as they will occupy only a portion of 

 our time, the following series have also been decided on : — 



1st. With a view to improvement in the constant of lunar parallax, 

 Burckhardt's semidiameter, and the local longitude, the moon and 

 culminating stars on the meridian ; both limbs at opposition and 

 near conjunction. 



2nd. The smaller planets on the meridian. 



3rd. A catalogue of stars to the 8th magnitude inclusive, within 

 60° of the south pole. 



Three hours of every suitable night will be given to this work, 

 and the arrangement is such that the whole 60° may be examined 

 and three observations made of each star within the proposed term 

 of residence. 



4th. Lunar occultations. Longitudes resulting from culminatio7is 

 as compared with occultations, have exhibited an extraordinary dif- 

 ference, to be accounted for perhaps by an error in the assumed 

 semidiameter ; this series of observations is considered necessary. 



5th. It has been thought that useful information to terrestrial re- 

 fractions will be obtained from observations in the two hemispheres 

 on circum-zenith stars at each place of observation, and six stars 

 have been selected which are near the zeniths of Talca and Wash- 

 ington to be observed on the meridian. 



6th. Comets when discovered in the course of other observations, 

 and at their periodic returns. 



7th. Magnetical observations. The term-days of such observa- 

 tories as continue to keep them has been set apart to obtain the three 

 elements of the earth's magnetic condition, and on occasional term- 

 days the observations would be made uninterruptedly during twenty- 

 four hours with the declinometer. 



8th. Meteorological observations at three stated hours (9 a.m., 

 3 p.m. and 9 p.m) of each day; to embrace records of barometer; 

 dry, wet, radiating and registering thermometers ; rain-gauge ; wind- 

 vane and clouds. Hourly observation on equinoctial and solstitial 

 term-days. 



9th. Earthquakes, the registrations of a seismometer. 



A meridian circle of 3 feet diameter, with a telescope of 52 lines 

 aperture, has been ordered from Pistor and Martins ; the Smithsonian 

 Institution has just authorized me to obtain an equatorial of 6 (French) 

 inches aperture, with clock motion, which they will lend me ; in ad- 

 dition to which I have a 48 lines equatorial by Fraunhofer ; these, 

 with a clock and one or two portable instruments, comprise my astro- 

 nomical equipment. In magnetism I am most especially desirous of 

 your advice. Pray give me all possible information, and recommend 

 such instruments, times and methods of observation as our limited 

 grant from congress and the number of assistants will enable me to 

 obtain and use as designated. 



