1864. | Physics. 497 
tions have been made with a view to some alterations in the French 
coinage system. An alloy prepared with 835 parts of silver, 93 parts 
of copper, and 72 of zinc, presents many advantages. The fact that 
this alloy is obtained by adding 77 grammes of zine to each kilo- 
gramme of the existing money, is considered a strong recommendation. 
All the alloys of silver with zine are found to be perfectly homoge- 
neous, and for coining possesses all the advantages which belong to 
the alloys of silver and copper, giving a metal, at the same time, of a 
fine white colour. 
An alloy of 850 parts of silver, with 150 parts of zine, is said, from 
its fine colour, to be well fitted for bijouterie.* 
IX. PHYSICS. 
Licut.—Since our last Chronicles of the progress of optical science, 
many interesting researches have been made, foremost of which should 
be mentioned the striking discovery by MM. Plucker and Hittorf, 
that certain bodies, such as nitrogen and sulphur, give two very 
different spectra, according to the temperature to which the incan- 
descent vapour is submitted. To show this, they pass through the 
tubes (containing the gas or vapour in a highly rarefied state) the 
ordinary current of an induction coil ; in this manner they obtain what 
is named the first spectrum, formed of large bands more or less regular, 
and often presenting the appearance of channelled spaces cut out by 
black rays. This corresponds to the lowest temperature. By inter- 
posing a Leyden jar, and varying the surface of this jar, the calorific 
action is likewise varied; in this manner, by gradually raising the 
temperature of the gaseous body, they find that at a certain point an 
essential modification takes place in its molecular constitution, and 
another and entirely different spectrum suddenly takes the place of 
the former one. This second spectrum, corresponding to the higher 
‘temperature, is generally characterized by brilliant rays on a more or 
less luminous ground. Sulphur shows in a striking manner the abrupt 
passage from one spectrum to the other. Upon gradually increasing 
the temperature, the first spectrum gets brighter and brighter ; when 
at the moment it attains its maximum of brilliancy, it suddenly disap- 
pears and gives place to the second spectrum, the richest in brilliant 
rays which the authors had ever seen. On lowering the temperature, 
the second spectrum disappears equally suddenly and gives place to 
the first. 
Nitrogen gives three spectra, showing three different molecular 
conditions. Naming these according to the general character of the 
bands they show, MM. Plucker and Hittorf consider that nitrogen has 
two distinct first spectra,—one of a yellow colour, corresponding to 
the less degree of incandescence, and the other of a blue colour, corre- 
* ¢Les Mondes, Revue Hehdomadaire des Sciences,’ tome iv. 15 livraison. 
* L'Institut, Journal Universel des Sciences.’ 
