C. GENERAL PHYSICS. 133 



area the square gives the gravest tone, and any membrane 

 not a circle is higher in pitch than the circle of equal area. 

 In estimating therefore the lower limit to the pitch of a reg- 

 ular polygon, it is best to substitute for it a circle of equal 

 area. Proc. London Mathematical Society, V., 9. 



THE SPECTRA OF THE LEAST FUSIBLE METALS. 



Messrs. Lockyer and Roberts have attempted to investi- 

 gate the nature of the absorption spectra of the least fusible 

 metals, for which purpose they employed the oxyhydrogen 

 blowpipe to volatilize the substances. Their experiments, 

 conducted at these high temperatures upon more than twenty 

 metals, go far, they think, to support the conclusions which 

 they had previously drawn from experiments at a lower tem- 

 perature on more easily volatilized metals, viz., that in pass- 

 ing from a liquid to the most perfect gaseous state, vapors 

 are composed of molecules of different orders of complexity, 

 and that this complexity is diminished by the disassociat- 

 ing action of heat, each molecular simplification being mark- 

 ed by a distinct spectrum. 



THE CAUSE OF THE VARIATION OF GASEOUS SPECTRA. 



The variations in the spectra of gases have been usually 

 supposed to depend to a certain extent upon the temperature 

 at which the light is produced. Wiillner has advanced the 

 theory that the spectrum depends upon the nature of the 

 electric spark ; but Goldstein has recently advanced opposite 

 views, to the effect that the different order of spectra are en- 

 tirely independent of the form of the electric discharge by 

 which the light is produced. He states that he has been 

 able to secure a notable increase in the width of the lines of 

 the spectrum of hydrogen when the pressure has been less 

 than one one-hundredth part of a millimeter. His experiments 

 lead him to think that any given order of spectrum can be 

 produced, if we only have a sufficiently high temperature. 

 19 <7, VII., 444. 



A SIMPLE SPECTROSCOPE FOR STARS. 



For the purpose of observing the spectrum of stars or 

 other points of light, Zullner describes a very compendious 

 instrument to be used in combination with the eye-piece of 



