of the Atmosphere, and on the Peculiarities of Stars. 329 



ployed is by the adaptation of the prism to the telescope and 

 by the use of a chromatopoietic lens. I have tried several 

 experiments with the prism adapted to different parts of the 

 telescope, and I have tried various methods with the lens, 

 which it is unnecessary to detail, as they are well known. 

 After all, I believe the best way is for each observer to pur- 

 sue his own method, and to give only the result at first; for 

 if it should turn out by a future comparison of results, that 

 any facts be ascertained by the employment of different means, 

 then would the said facts be established on the firmest basis. 

 I have myself employed several modes of observation, and 

 they have certainly all agreed in this, that they have shown 

 the same relative degree of oblongation of the spectrum, or 

 the same apparent proportion of the coloured rays of each 

 star respectively ; none of the different methods employed have 

 contradicted each other*, and the variety in the results on dif- 

 ferent nights of observation has been distinctly referable to 

 the varieties in the dispersive qualities of our atmosphere, 

 which I have already discussed in a former part of this me- 

 moir. Making allowance for these slight varieties, which 

 my constant attention to atmospheric phasnomena has enabled 

 me in many cases to foresee and prepare for, the same star 

 in the following Table has always shown the same phaeno- 

 mena. Those stars which seem to vary in consequence as it 

 would seem of some changes going on in their own proper 

 light, or which are anomalous and incapable of being in- 

 cluded in the same general view of the subject, have been put 

 apart by themselves and will be mentioned hereafter. 



In the Table, column 2, I have put down the apparent 

 colour of the stars, not only as observed in general with the 

 naked eyes, but by the employment of another and very sim- 

 ple method. I pushed the eyeglass of a four feet refractor 

 gradually in, so as to let the rays fall on the glass before they 

 came to a focus; — this method if applied to terrestrial objects 

 in the day time would only produce confused images, and 

 utterly defeat the intentions of the beholder. From this cir- 

 cumstance its use at night has been probably overlooked : for 

 as applied to brilliant luminous points it is of considerable 

 use. I usually pushed in the adjusting tube of the tele- 

 scope, till I obtained a large round spectrum of the star, so 

 expanded that it occupied a large space in the field of view. 

 This method will answer very well for all very bright stars, 

 because what we lose in the dazzling intensity of the light 



* It was by an error of calculation that I placed Sinus first in the scale af 

 refrangibilky in my former paper in Phil. Mag. No. 311, page 203. 



Vol. 63. No. 313. May 1824. T t when 



