xlii GENERAL SUMMARY OF SCIENTIFIC AND 



Observations suggested by Janssen have resulted in show- 

 ing that the two dark bands in the solar spectrum, on either 

 side of the D line, disappear at the altitude of from 6000 to 

 7000 meters, reached in a balloon. This shows that these 

 lines are due to the absorptive action of our atmosphere, 

 and not to the action of moisture in the sun's atmosphere, as 

 maintained by Secchi. 



Villari has investigated the time required by magnetic cur- 

 rents to rotate the plane of polarization of a ray of light 

 passing through glass. 



Becquerel has succeeded, by using chlorophyl after the 

 manner of Dr.Vogel, in obtaining a photograph of the spec- 

 trum much longer than that given by plain collodion, and 

 confirming Vogel's statement that plates sensitized with io- 

 dide or bromide of silver may, by a proper varnish, be made 

 sensitive to other than the extremely refrangible rays. 



In the department of Spectroscopy, Professor Eaton, of 

 Philadelphia, proposes a simple modification of the spectro- 

 scope, by means of which the dispersion is increased fourfold. 

 The origin of the curvature of the transverse lines of the 

 spectrum has been investigated by Christie, of Greenwich 

 Observatory, and a method of reflection suggested by means 

 of which it may be counteracted. The equally simple meth- 

 od of a curved slit has been practiced by some English mak- 

 ers. Lockyer has continued his spectroscopic studies bear- 

 ing on the chemical constitution of bodies including the so- 

 called simple elements; and somewhat more attention has 

 been given than hitherto to the very important modifications 

 of the spectrum depending on the temperature of the radiat- 

 ing and absorbing bodies. 



Croullebois describes an ingenious arrangement by means 

 of which he is able to determine exactly the ellipticity of 

 the vibrations of homogeneous elliptically polarized light. 



As a simple camera, for convenience in drawing, Govi pro- 

 poses to use a plate of glass covered with a thin film of gold 

 or silver, a device that has been already in use in this coun- 

 try and France. 



It is announced that a method has been devised, we pre- 

 sume at the works of Messrs. Chance & Co., by means of 

 which perfectly achromatic objectives can be constructed of 

 a lens of the terborate of lead, combined with others formed 



