[ 78 1 

 X. Intelligence and Miscellaneous Articles. 



ON A NEW PHOTOMETER. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, Melton, December 16, 1867. 



f REGRET to find that I have stated ^ inch as the size of the 

 -*- diaphragm y, it should be -^ inch : this is not your printer's fault, 

 but my own. 



Perhaps the limit of darkness at which a thing can be seen varies in 

 different people, so that the observer must to some extent determine 

 for himself the size of the diaphragms. Instead of the microphoto- 

 graph, I now prefer tissue paper at x, and a strong convex lens at its 

 principal focus behind x in B. A transparent glass picture varying 

 in depth of shade lies between the lens and the microscope A. 

 With many apologies for the space I have taken, 

 I am, Gentlemen, 



Your obedient Servant, 



C. H. Bennington. 



NEW OBSERVATIONS ON THE SPECTRA OF THE FIXED STARS. 

 BY FATHER SECCHI. 



In some previous communications I have shown that the spectra 

 of the fixed stars may be referred to three characteristic types, repre- 

 sented (1) by aLyrae (Vega), (2) by a Herculis, and (3) by a Boots) 

 (iVrcturus), or by our sun itself. Between the first and the last ca- 

 tegory nearly all the stars already investigated are pretty equally 

 divided. 



These results deserved to be confirmed by more comprehensive 

 and more numerous observations ; and these I have made. Upwards 

 of 500 stars, the largest in the heavens, have been examined from 

 the Observatory of the Collegio Romano ; and I have given a com- 

 plete description of more than 400 of them. 



The details of this investigation are not less interesting. The first 

 type, a Lyrse, contains in fundamental lines two very distinct hydro- 

 gen rays — that, namely, in the blue which coincides with the solar 

 line/", and one in the violet, which, as far as I can conclude from M. 

 Pliicker's investigation of hydrogen, coincides with the line H y. 

 The line H a or C is seldom visible ; for the red is either absent in 

 this type, or is at any rate very feeble. 



M. Pliicker has shown that the hydrogen lines H/3 and Hy are 

 broader at higher temperatures (and that the lines in question are 

 present in these stars is indicated by their breadth), and that the one 

 in the violet is always broader than that in the greenish blue. In some 

 stars these lines are somewhat diffused, which M. Pliicker has also 

 found to be the case with hydrogen lines when the temperatures 

 and pressures are considerable. 



