378 



Miscellanies. 



seems no means of accounting for the prodigious force then exerted 

 to sustain a column of water of such height except that which as- 

 cribes it to a current or whirhvind of excessive intensity. — Bib. 

 Univ. 1833. 



NATUKAL PHILOSOPHY. 



1. Description of a Photometer, designed for comparing the splen- 

 dor of the stars ; by Count Xavier De Maistre. — This instrument 

 is composed of two cuneiform prisms, one of blue and the other of 

 white glass, which, when placed one on the other, form a parallelo- 

 piped. The aperture of the angle of the prisms is 11°, and their 

 length nine English inches. These dimensions admit of variation. 



The beak of the blue prism is so thin that it transmits the light of 

 the smallest stars, whilst its other extremity, which is eight lines thick, 

 is not permeable to their hght. In moving it along, by degrees, 

 the different stars will disappear at different distances from the point, 

 according to their splendor. The refractions of the oblique surfaces 

 of the compound prism compensate each other, which affords the 

 means of looking for the star by a finder in making use of large tel- 

 escopes, the narrow end only of the blue prism being adjusted before 

 the eye glass, and the blue prism moveable on the line cd. 



By increasing the angle of the prism or the intensity of its color, 

 it may be applied to more luminous objects. 



This photometer has an advantage rarely possessed by instruments 

 used for this purpose ; it is perfectly comparable. In taking the 

 Ijfht of some one star of the first magnitude for a maximum, the 

 point on the prism where it disappears must be marked, and the dis- 

 tance between this point and the beak divided into an hundred equal 

 parts, which would of course always be proportional to each other 

 in every prism, (as are the degrees on the scales of different ther- 

 mometers,) and thus the exact relation of the light of any star to 

 that of another may be determined. 



This instrument may be substituted for smoked glass in solar ob- 

 servations by the facility of altering at pleasure the intensity of the 



