A. MATHEMATICS AND ASTRONOMY. 45 



est for the vapors of greatest density, highest for the hydro- 

 gen ; and far above these towers the matter of the corona. 

 The upper surface of the chromosphere has a form as irregu- 

 lar and fantastic as a sheet of flame, and it is probable that 

 the wild commotion that exists within it is accompanied by 

 a development of electric force abundantly sufficient to ac- 

 count for all the observed resemblances between the corona 

 and the electrical phenomena of our atmosphere. Report of 

 the Superintendent of the Coast Survey, 1870, p. 115. 



ABSORPTION SPECTRA AT LOW TEMPERATURES. 



Roscoe has made some observations looking to the deter- 

 mination of the peculiarities of the absorption spectra of po- 

 tassium and sodium at low temperatures. By means of a 

 large Steinheil spectroscope, he detected in the green vapor 

 given off by potassium a complicated absorption spectrum 

 of three bands in the red and yellow, each shading offtoward 

 the red, and in general resembling those of iodine. Similar- 

 ly, the vapor of sodium, which when seen in thin layers ap- 

 pears nearly colorless, exhibited absorption bands in the blue, 

 red, yellow, and orange, each shading offtoward the red, as 

 in the potassium bands before noticed. 12 A, X., 1874,136. 



NEW METALLIC ELEMENTS IN THE SOLAR ATMOSPHERE. 



Lockyer, in a preliminary report on the elements that have 

 been found in the solar atmosphere, has shown that besides 

 the zinc and aluminum rediscovered by Thalen, it is also 

 probable that strontium, cadmium, copper, and cerium exist 

 therein. If, now, it appears that cerium and uranium are 

 really present there, it would follow that the entire group of 

 " iron metals" occurs in the solar atmosphere. IleW Wochen- 

 schrift, 1874, 150. 



A STRIKING SUN-DIAL. 



A sun-dial that strikes the hours has lately been invented 

 and constructed by the Abbe Allegret. It is simply a modi- 

 fication of what is known as the solar counter for registering 

 the times at which the sun shines or is obscured. To effect 

 this there are two balls, one black and the other yellow, fix- 

 ed at opposite ends of a lever, sustained by a central pivot. 

 When the sun shines, the black ball absorbs more heat than 



