1815.] Scientific Intelligence. ~ 75 
he had himself taken, not one measured 65 feet in length. In the 
North Pacific, however, the size is often much larger than this; 
for Capt. Clarke measured the skeleton of one near Columbia river, 
and found it 105 feet in length. (See Travels to the Source of the 
Missouri, &c. by Captains Lewis and Clarke, p. 422.) 
IX. Inhabitants in Ancient Rome. 
In ancient Rome the number of insule, or houses, standing 
separately, was 46,000 in the time of Trajan. The domus (pro- 
bably the principal buildings or palaces of Rome), 1800. The 
houses of Rome were usually four stories high. If we suppose, with 
Gibbon, that each story lodged a family of six persons, each of the 
insule would contain 24 inhabitants. ‘his would give us the whole 
inhabitants of Rome at 1,113,448; so that the population of 
ancient Rome, when greatest, exceeded the present population of 
London by about 60,000. (See Gibbon’s Posthumous Works, v. 318.) 
X. Extract of a Letter from M. Van Mons, of Brussels. 
I take this opportunity of sending you some curious information 
which I have just learned by a letter from the discoverer. 
If indigo in powder be thrown upon red hot charcoal or iron, a 
fine violet coloured vapour rises, which Brugnatelli at first took 
for iodine. This vapour when condensed crystallizes in four-sided 
prisms very brilliant and of a fine violet colour. ‘To this substance 
Brugnatelli gives the name of indigogen, because when united to 
the fecula of the plant it forms indigo.* He considers it as a me~ 
tal, because if mercury be exposed to its vapour a combination 
takes place, which is hard or soft according to the proportion of 
the indigogen, and which possesses the properties of an amalgam. 
Indigo deprived of this substance loses the property of acquiring a 
cupreous lustre by friction. ‘The new substance is found in every 
variety of indigo. 
Brugnatelli has observed that ice when rasped becomes positively 
electric. ‘This confirms the notion that its conducting power fol- 
lows immediately that of the metals. Pure water, or water exempt 
from all salt, is almost a non-conductor. Brugnatelli was unable 
to construct a galvanic battery by uniting ice with any metal which 
he tried. 
Zamboni at present draws strong sparks, and gives shocks with 
the dry galvanic column, But I venture to predict, that it will 
never be able to produce chemical effects, where an abstraction of 
electricity is requisite. ‘The charge may circulate without water, 
but cannot be renewed, 
Volta has just obtained electric fluorine in considerable quantity. 
Configliachi is the editor of it.t 
Gay-Lussac believes that euchlorine or your oxide of chlorine 
* It has been known to chemists for many years. T, 
+I do not understand the meaning of the sentence, The original is Configli- 
achi en est Vediteur. 
