226 DIRECTIONS FOR OBSERVING 



fact during my sojourn at the Great St. Bernard. Is it always the 

 case ? 



S. Accessory observations. — That observations made upon the subject i 

 in question may be really valuable, it behooves us that they should 

 be accompanied by meteorological observations 'as complete as pos- 

 sible. Let the indications of the barometer, the thermometer, and : 

 the hygrometer at least be noted, as well as the state of the sky and I 

 the force and direction of the wind. It is probable that in the 

 localities where scintillation will be observed, meteorological obser- 

 vations will also be made and published; whence I presume it will I 

 not be devolving on observers any great increase of occupation if 1 

 the}' be persuaded to combine the records which have been made • 

 for the study of meteorology with those collected for the study of 

 scintillation. 



There remain, doubtless, a number of other details, depending on i 

 the views of the observer and the circumstances in which he is ^ 

 placed — details which I omit because they will naturally vary with i 

 each individual. I am content with liaving indicated the principal I 

 subjects to which I would call the attention of observers, and whose ; 

 importance has been disclosed to me by experience. 



I may be allowed, in conclusion, to address to those who shall be 

 disposed to observe the scintillation of the stars, particularly to those 

 residing in any climate greatly differing from that of Morgcs, the 

 earnest request that they will communicate lo me a brief summary of t 

 their observations. That the results at which they arrive will be of I 

 the highest interest to me none can doubt, and the courtesy will be :. 

 gladly reciprocated on my part by furnishing other details to such as ij 

 may be induced to engage in these researches. 



I may state, in addition to what has been said in the foregoing 

 article on the subject of the planets, that I have seen Jupiter and I 

 Venus distinctly scintillate, the last particularly, on the 3d of January, 

 1841, when the weather was stormy and the barometer rapidly sink- 

 ing. The feeble scintillation of the stars was, I remember, quite 

 striking when I viewed them from the elevation of the Faulhorn. 



I propose to give, in future numbers of the " Repertorium," various 

 instructions for the observation of phenomena which are seldom the 

 subject of investigation, such as the polarization of the light reflected 

 by the atmosphere. In many phenomena this plays a more consid- 

 erable part than is generally l3elieved, and since, in observations upon 

 Donati's comet, the assertion has been frequently made that its light 

 was polarized, as was determined also by Arago with regard to the 

 comets of 1819 and 1835, I take occasion to cite the following remarks 

 of Brewster, which occur in the " Comptes Rendus" of the Academy i 

 of Sciences, XLVIII, 384: "I am not aware that those who have ob 

 served traces of polarization in the light of comets have noticed the 1 

 direction of the plane in which it was polarized. Without such an 

 observation, however, we cannot discover the cause. If the light is ■ 

 polarized in a plane passing by the sun, the comet, and the eye, we i 

 must infer that it is polarized by the reflection of the light coming j 



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