BIS 
The acid employed for this purpose must 
be one that does not act on paper, such as 
the acetic. Characters written with this 
solution become visible when exposed to 
sulphuretted hydrogen. 
BISECTION, in geometry, the division 
of a line, angle, &c. into two equal parts. 
BISSEXTILE, or leap-year, a year 
consisting of 366 days, and happening every 
fourth year, by the addition of a day in the 
month of February, which that year consists 
of 29 days. And this is done to recover the 
6 hours which the sun takes up nearly in 
his course more than the 36o days com- 
monly allowed for it in other yeais. 
The day thus added was by Julius Caesar 
appointed to be the day before the 24th of 
February, which among the Romans was 
the 6th of the calends, and which on this 
occasion was reckoned twice; whence it 
was called the bissextile. By the statute 
De anno bissextile, 21 Hen. III. to prevent 
misunderstandings, the intercalary day and 
that next before it are to be accounted as 
one day. 
To find what year of the period any given 
year is, divide the given year by 4, then if 0 
remains it is leap year; but if any thing 
remain the given year is so many after leap 
year. But the astronomers concerned in 
reforming the calendar in 1582, by order of 
Pope Gregory XIII. observing that in 4 
years the bissextile added 44 minutes more 
* than the sun spent in returning to the same 
point of the ecliptic ; and computing that 
in 133 years these supernumerary minutes 
would form a day ; to prevent any changes 
being thus insensibly introduced into the 
seasons, directed that in the course of 400 
years there should be three sextiles re- 
trenched; so that every centesimal year, 
which is a leap year according to the Julian 
account, is a common year in the Gregorian 
account, unless the number of centuries can 
be divided by 4 without a remainder. So 
1600 and 2000 are bissextile; but 1700, 
1800, and 1900 are common years. 
The Gregorian computation has been 
received in most foreign countries ever 
since the reformation of the calendar in 
1582, excepting some northern countries, 
as Russia, &c. And by act ot pailiament 
passed in 1751, it commenced in all the 
dominions under the crown of Great Britain 
in the year following ; it being ordered by 
that act that the natural day next following 
the 2nd of September should be accounted 
the 14th; omitting the intermediate 11 days 
of the common calendar. The supernume- 
BIT 
rary day in leap years being added at the 
end of the month February, and called the 
29th of that month. 
BISTOURY, in surgery, an instrument 
for making incisions, of which there are dif- 
ferent kihds, some being of the form of a 
lancet, others straight and fixed in the han- 
dle like a knife, and others crooked with 
the sharp edge on the inside. 
BISTRE, or Bister, among painters, 
denotes glossy soot, pulverised and made 
into a kind of cakes with gum-water. 
BIT, or Bitts, in ship-building, the name 
of two great timbers usually placed abaft 
the manger in the ship’s loof, through which 
the cross-piece goes ; the use of it is to 
belay the cable thereto while the ship is at 
anchor. 
BITCH, the female of the dog kind. See 
Canis. 
BITTER, a sea term, signifying any turn 
of the cable about the bits, so as that the 
cable may be let out by little and little. 
And when a ship is stopped by a cable she 
is said to be brought up by a bitter. Also 
that end of the cable which is wound about 
the bits is called the bitter end of the 
cables. 
Bitter principal. The bitter taste of 
certain vegetables appears to be owing to 
the presence of a peculiar substance, differ- 
ing from every other in its chemical pro- 
perties. It may be extracted from the 
wood of quassia, the root of gentian, the 
leaves of the hop, and several other plants, 
by infusing them for some time in cold 
water. The characters of this substance, 
originally described by Wether, have been 
attentively examined by Dr. Thomson, who 
enumerates them as follows. 1. When 
water thus impregnated is evaporated to 
dryness by a very gentle heat, it leaves a 
brownish yellow substance which retains a 
certain degree of transparency. For some 
time it continues ductile, but at last becomes 
brittle. Its taste is intensely bitter. 2. When 
heated it softens, swells, and blackens ; then 
burns away without flaming much, and 
leaves a small quantity of ashes, o. It is 
very soluble in water and in alcohol. 4. It 
does not affect blue vegetable colours. 5i It 
is not precipitated by the watery solution of 
lime, barytes, or strontites ; nor is it chang- 
ed by alkalies. 6. Tincture of galls, infu- 
sion of nut-galls, and gallic acid, produce 
no effect. 7. Of the metallic salts, nitrate 
of silver and acetate of lead are the only 
ones that throw it down. The precipitate 
by acetite of lead is very abundant ; and 
