Physics. 411 
give the same reaction with both classes of salts.” Among the difficulties 
encountered is named this one, “the nitrites are generally either de- 
: adi : 
care required in making this test, the following words are found: “ With 
these precautions, I have found this test astonishiigly delicate, in fact 
“sate with those for iron, iodine, &c. Using fused nitre, I have de- 
tected the presence of 1 pt. in 617, 000 pts. of water; a bystander, wholly 
ignorant of the nature of the operation, pronouncing as to the color. Yet 
this salt contained about one-half its weight of undecomposed nitre.” 
It is very doubtful eres an er notice than this, of the presence 
of nitrites in rain-water. ee 
on the continent, and, as the much valued Reports of the Smithsonian 
Institution are widely distributed, the verification of the quotations above 
cited can readily 
It is a matter of regret that = want of time and the absence of docu- 
mentary evidence, soon to b2 supplied, prevents, at present, the continu- 
ation e my eotiteibations to the history of this subject as connected with 
cal science; since the result, it is believed, would show another and 
an sattiée origin "for these views than any which has yet been assigned 
_ to them 
—_— 
SCIENTIFIC INTELLIGENG e- 
I, PHYSICS. 
e 
- The electrical spectrum is =gevioa tees of two ee spectra, the 
one belonging to the metal of the electrodes, the other to the gas through 
. ct spark passes, the two spectra being distinguishable by the dif- 
2 in appearance. Metallic compounds and metallic sulphids have 
_ ote their luminous spectra the same lines as each of the bodies which 
the und contains, and this affords a ready method of qualitative 
