NATURAL PHILOSOPHY. 135 



surface. It would be curious to try lights of different colors, and to 

 see if the process could not be accelerated by exposing the negative 

 paper to a certain quantity of light, either after it has received a faint 

 picture, or before it is placed in the camera. If M. Evrard's results 

 are correct, there must be some new principle called into play by the 

 supplementary light assisting the natural light from the object." 

 Daguerrean Journal. 



DAGUERREOTYPES OF THE SUN AND MOON. 



DURIXG the past season, Mr. J. A. Whipple, of Boston, aided by 

 Mr. Bond, of the Cambridge Observatory, has succeeded in taking sev- 

 eral large and beautiful daguerreotype likenesses of the moon, as seen 

 by a high power, under the great equatorial of the Observatory. We 

 have rarely seen anything in the range of the daguerreotype art of so 

 great beauty, delicacy, and perfectness, as the pictures referred to. 

 The inequalities and striking peculiarities of the moon's surface are 

 brought out with such distinctness, that the various mountain ranges, 

 highlands, and isolated peaks are at once recognized. Crater-formed 

 depressions in some of the mountains may be also seen. The views 

 represent the moon at quarter and half-quarter, and are from three to 

 four inches in length. Mr. Whipple, with the aid of Mr. Bond, suc- 

 ceeded in daguerreotyping the solar eclipse of July, in its various 

 stages ; and also the sun's disk, with the various spots which appeared 

 upon its surface in the spring of 1851. Several of these daguerreo- 

 types were exhibited at the American and British Associations, and 

 also at the Great Industrial Exhibition, where a medal was awarded 

 to Mr. Whipple. Editor. 



NEW ELLIPTIC ANALYZER. 



A NEW instrument, constructed for the purpose of investigating ex- 

 perimentally the nature of elliptically polarized light, that is to say, 

 the elements of the ellipse described, has been invented by Professor 

 Stokes, of England. In its exhibition before the British Association, 

 Prof. Stokes said, that, in its construction, he had aimed at being, in 

 all important points, independent of the instrument-maker, assuming 

 nothing but the accuracy of the graduation. The construction was as 

 follows : A brass rim, or thick annulus, is fixed on a stand, so as to 

 have its plane vertical. A brass circle, graduated to degrees, turns 

 round within the annulus, and the angle through which it is turned is 

 read by verniers engraved on the face of the annulus. The brass circle 

 is pierced at its centre, and carries on the side turned towards the inci- 

 dent light a plate of selenite, of such a thickness as to produce a differ- 

 ence of retardation in the oppositely polarized pencils, amounting to 

 about a quarter of an undulation for rays of mean refrangibility. The 

 brass circle carries a projecting collar on the side next the eye, and, 

 round this collar there turns a movable collar carrying verniers, and 

 destined to receive a Nicol's prism. The observation consists in extin- 

 guishing the light by a combination of the two movements. The 



