1 98 Instructions for the Scientific Expedition 



of much of their tedium, and to reward by the frequent detection of 

 variable stars not previously recognized as such. 



10. Refraction. 



The determination of refractions near the horizon, both of celes- 

 tial and terrestrial objects in high southern latitudes, will form a 

 very interesting subject of study. They may be pursued in various 

 modes, of which perhaps the easiest is to note the disappearance of 

 particular stars behind the horizontal edge of a board, erected at 

 some considerable distance from a fixed point of observation, and 

 then to ascertain, with all precision, the altitude of the line of dis- 

 appearance, accompanying such observation with the height of the 

 barometer and thermometer. Vertical diameters of the sun or moon, 

 when very near the horizon, with the corresponding altitudes, will 

 also be of use, as well as measurements of the distances of two con- 

 siderable stars on the same vertical, and direct measures of the alti- 

 tudes of one and the same star in the progress of its diurnal course 

 when near the horizon. The curve of terrestrial refraction might 

 also be actually traced out by a leveling-stafF. Any cases of un- 

 usual refraction, mirage, reduplication and inversion of images, and 

 of lateral refraction, should be recorded. 



11. Eclipses. 



In annular or total solar eclipses the optical circumstances attend- 

 ing the formation and rupture of the ring should be minutely attended 

 to, as well as the defalcation of light and heat, to be measured by 

 their appropriate methods, as detailed in the Meteorological instruc- 

 tions. 



m, 1 V e r January 11, 1842 



The solar eclipses of | j^^^ ^^^ ^g^^ 



may possibly be central, or very large in some part of the progress 

 of the Expedition. In lunar total eclipses the occultations of stars, 

 whether large or small, should be looked for, and any apparent pro- 

 jection on the disk noticed. Great attention should also be paid to 

 the intensity, colour, and distribution of illumination over the disk 

 during the toto/ eclipse, as indicative of the general stoieoitheeartJis 

 atmosphere in that great circle of the globe which at the moment is 

 at right angles to the visual ray. 



As a summary of this Report, the Council recommend to the Ad- 

 miralty to give instructions for the making and recording of the 

 following observations, experiments, and researches. 



1. Magnetic observations of the inclination, declination, and in- 

 tensity at sea, throughout the voyage, daily in both ships, whenever 

 the motion of the vessel will permit. 



2. Precise determinations of the same particulars wherever the 

 Expedition may land, or disembark on ice. 



3. Most careful series of magnetometric observations, in corre- 



