462 SCIENTIFIC RECOKD FOR 1884. 



with the angle of emission, though in a nearly normal direction the 

 rays have the same intensity. Behind the diffuser an opaque screen is 

 fixed, furnished with a variable slit. The amount of light passing through 

 this opening is proportional to the extent of the luminous field covered 

 by it, to a coefQcient depending on the diffuser itself, to the area of the 

 opening, and to the inverse square of the distance. By means of such 

 a photometer the author has determined the sun's light to be equal to 

 7,500 carcels, that of the Serrin lamp used by him being 230 to 320 

 carcels. The coefficient of his diffuser is the value in carcels of the 

 field in which the diffuser should be placed in order that 1 sq. cm. of 

 its surface should emit the light of one carcel. Thus a ground glass of 

 400 carcels is a glass 1 sq. cm. of which placed in a field of 400 carcels 

 emits a light of 1. {G. R., December, 1884, xcix, 1115.) 



McLeod has proposed a new sunshine-recorder, consisting of a camera 

 so fixed that its axis is parallel to the polar axis of the earth, the lens 

 pointing northward. Opposite the lens a silvered sphere is placed, from 

 which the rays of the sun are reflected through the lens of the camera 

 on to the sensitive paper, on which a distorted image of the sun is formed, 

 the positions of the lens and sphere being so arranged that the image 

 is a linear and radial one. By the motion of the earth the solar image 

 is carried over a circular arc, and traces a curve on the sensitive paper. 

 The ordinary ferricyanide paper is employed, and the instrument is 

 sufficiently sensitive to register gleams of sunshine and also the pas- 

 sage of small clouds. Eadial lines are drawn from the center of the cir- 

 cular band, 15° apart, to serve as hour lines. {Phil. Mag., Atigust, 1884, 

 V, XVIII, 141.) 



2. Beflection and Refraction. 



Basso has studied the phenomena of reflection from crystalline sur- 

 faces, using a Bunsen photometer illuminated on one side by sunlight 

 which has traversed orange-yellow glass, and is polarized in a suitable 

 azimuth by means of a Nicol prism, reflected to the screen from the 

 crystalline face to be studied, the other side receiving the light from a 

 disk of ground glass, illuminated by a petroleum lamp. The crystal 

 used was a plate of Iceland spar, cut perpendicularly to the axis. The 

 intensity of the light reflected from the spar was calculated for various 

 angles of incidence and for various azimuths of polarization. For azi- 

 muth the formulas become those of Fresnel. Assuming the value 

 for this azimuth and rotating the Nicol, the intensity may be determined 

 for various azimuths by varying the distance of the lamp from the disk. 

 The results are in fair accord with theory. {II Nuovo Gimento, xiv, 5 ; 

 J. Phys., December, 1884, II, in, 558.) 



Conroy has communicated to the Eoyal Society the results of his 

 measurements of the amount of polarized light reflected by metallic 

 surfaces. He used mirrors of steel and of speculum metal, highly pol- 

 ished, the incident light being polarized by a Isiicol prism. The expert* 



