S L I 
slide on the lower mast: the peek or head is attached to a 
small top-mast, that slides up in the direction of the lower 
mast, through two hoops fixed at its head, about three feet 
asunder. When the top-mast is lowered, the sail furls up 
close to the lower mast. 
SLIDING-PLANKS, are the fiat forms upon which the 
bilgeways slide in launching the ship. 
SLIDING-RULE, a mathematical instrument, serving to 
work questions in gauging, measuring, &c., without the use 
of compasses; merely by the sliding of the parts of the in¬ 
strument one by another, the lines and divisions of which 
give the answer, by inspection. 
To understand the use of this instrument we must recur, 
to what is already familiar to the reader—the nature and use 
of logarithms; namely, the rapid manner in which multi¬ 
plication, division, and the like may be performed by simple 
addition or subtraction. 
Now the abbreviation of arithmetical calculations, usually 
attained by the use of logarithms, is also attainable by the 
employment of lines as the representatives of logarithms; 
so that by measuring these lines with their sums, differences 
or multipliers on a given scale, we may obtain a tolerable 
degree of accuracy. A farther improvement consists in 
graduating a line of convenient length logometrically, that 
is dividing it so that the distance of each division from the 
beginning of the line which is marked with unity, shall 
measure on a given scale of equal parts, the logarithm of the 
number which is affixed to it; this is Gunter’s scale. 
The divisions which are situated at equal distances, being 
marked by numbers whose logarithms have equal dif¬ 
ferences, it follows that the spaces intervening between any 
two numbers are proportional to the differences between 
their respective logarithms; or are the measures of the 
ratios between each of these numbers. The same use may 
therefore be made of such a scale as of a table of logarithms 
with regard to operations to be performed on their cor¬ 
respondent numbers. Thus it will be found that the portion 
of the scale extending from one to three, added to that 
extending from one to four, is equal to that between one and 
twelve, shewing that the logarithm of three, added to the 
logarithm of four, is equal to the logarithm of twelve, or 
that the ratio of one to three, added to the ratio of one to 
four, composes the ratio of one to twelve, or that twelve is 
the product of three and four. The excess of the interval 
between one and twenty-four, over that between one and 
six, or which is the same thing, the interval between six and 
twenty four, will be equal to that between one and four, 
shewing that four is the quotient of twenty-four divided by 
six. This comparison of intervals is further facilitated by 
the addition of a second scale exactly marked like the first, 
but capable of being slid along its side. Now, supposing 
the sides coincident, and the slider (he lowest, if we push the 
slider on to any given distance, each of its divisions will be 
brought under those of the fixed scale, which are before situ¬ 
ated further forward by an interval equal to that given dis¬ 
tance. Every number of the upper will then have a con¬ 
stant ratio to every number of the slider ; a ratio indicated by 
the number under which unity or the commencement of the 
slider is found placed. 
The upper numbers then will, by multiples of the inferior, 
bring this constant number. So that by adjusting the slider 
till unity stands under any given multiplier or divisor, the 
upper line will exhibit the series of products of all the 
subjacent numbers, by the given multiplier; and con¬ 
sequently the slider exhibits the series of the quotients 
resulting from the division of the numbers immediately 
above them by the given divisor. For in every position of 
the slider, all the fractions formed by taking all the numbers 
on the upper line as numerators, and those just under them 
as denominators, are equal. 
This instrument has been modified, and applied to the 
mensuration of timber and other solid bodies, to gauging, 
by Dr. W ollaston to the determination of chemical 
equivalents, and by Dr., Rojet to the involution and 
evolution of numbers. For the last, which is extremely 
S L I 287 
important, we must refer to the author’s excellent paper in 
the Phil, Trans. 1815., Part I. 
SLIEBH-AN-ERIN, mountains of Ireland, in the county 
of Leitrim ; 13 miles north-north-east of Carrick. 
SLIEBH-BAUGH, mountains of Ireland, in the counties 
of Monaghan and Tyrone ; 3 miles south of Clogher. 
SLIEBH BAUGHTA, mountains of Ireland, in the coun 
ties of Clare and Galway; 20 miles south-east of Galway. 
SLIEBH-BEARNA, mountains of Ireland, in the county 
of Down, near the sea coast; 14 miles east of Newry. 
SLIEBH-BLOOM, mountains of Ireland, in King’s and 
Queen’s counties. The high and steep mountains of Sliebb- 
bloom form so impracticable a barrier between King’s and 
Queen’s counties, that in a range of 14 miles, they afford 
but one, and that a very difficult and narrow pass into King’s 
county, called the Gap of Glandine. In this great ridge 
are the sources of the Barrow and the Nore. 
SLIEBH-BONN, mountains of Ireland, in the county of 
Roscommon ; 8 miles north-north-east of Roscommon. 
SLIEBH-BUY, mountains of Ireland, in the county of 
Wexford; 9 miles west of Newborough. 
SLIEBH-CROOBE, mountains of Ireland, in the county 
of Down ; 9 miles west-north-west of Downpatrick. 
SLIEBH-DHAM, mountains of Ireland, in the county of 
Sligo; 16 miles south-west of Sligo. 
SLIEBH-DONALD, mountains of Ireland, in the county 
of Down, near the sea-coast, said to be above 3000 feet 
higher than the level of the sea ; 14 miles east of Newry. 
SL1EBH-EAN, mountains of Ireland, in the county of 
Antrim; 18 miles north of Antrim. 
SL1EBH-EN-EWR, mountains of Ireland, in the north¬ 
west part of the county of Leitrim; 10 miles north-north¬ 
east of Sligo. 
SLIEBII-GALLAN, mountains of Ireland, in the county 
of Londonderry ; 5 miles west of Magherafelt. 
S LIEBH-GALLEN, mountains of Ireland, in the southern 
part of the county of Armagh ; 5 miles north of Dundalk. 
SLIEBH-LEAGUE, mountains of Ireland, in Donegal- 
shire ; 8 miles west of Killybegs. 
SLIEBH-LOGHER, mountains of Ireland, county of 
Kerry ; 9 miles south-east of Killarney. 
SLIEBH-MISH, mountains of Ireland, in the county of 
Kerry, between Tralee and Miltovvn; 4 miles south of 
Tralee. 
SLIEBH-MORE, mountains of Ireland, in the county of 
Mayo, near the western extremity of Achil island, near 
Achil Head. 
SLIEBII-NA-COILTRA, mountains of Ireland, in the 
county of Wexford; 2 miles south-east of New Ross. 
SLIEBH-NA-MAN, mountains of Ireland, in the county 
of Tipperary ; 7 miles north-east of Clonmel. 
SLIEBH-RUSSEL, mountains of Ireland, in the counties 
of Cavan aud Fermanagh; 12 miles south of Enniskillen. 
SLIEBH-SNAGHT, mountains of Ireland, in the county 
of Donegal; 13 miles north of Londonderry. 
SLIEDRECHT, a small inland town of the Netherlands, 
in the province of South Holland, with 2400 inhabitants. 
SLIGHT, adj, [slicht, Dutch.] Small; worthless; in¬ 
considerable. 
Their arms, their arts, their manners I disclose. 
Slight is the subject, but the praise not small, 
If Heaven assist, and Phcebus hear my call. Drj/den, 
Not important; not cogent; weak.—Some firmly em¬ 
brace doctrines upon slight grounds, some upon no grounds, 
and some contrary to appearance. Locke. —Negligent ; 
not vehement; not done with effort. 
He in contempt 
At one slight bound high overleap’d all bound. Milton. 
Foolish ; weak of mind. 
No beast ever was so slight 
For man, as for his God, to fight. Hudihras , 
Not strong; thin; as, a slight silk. 
SLIGHT, 
